The reason is that each social network is coming from -- and going to -- a completely different place.
We categorize things weirdly in this business. We lump giant, massively featured, multi-purpose do-everything-for-everybody sites like Facebook and Google+ in with tiny, narrow, single-purpose sites like Instagram or Twitter into the same category because they're all "social." It's like comparing a car with a skateboard because they're both "transportation."
In reality, there are only two major all-purpose social sites: Facebook and Google+. A GlobalWebIndex study published this week found pretty much what you'd expect: Facebook is much larger, but shrinking (losing 3% in the second half of last year), and Google+ is smaller but growing (gaining 6% in the same period). Google+ has roughly half the active user base of Facebook, according to the report.
Yet these two sites are embracing opposite strategies for the future. Specifically, Facebook is an integrated social network that is trying to become many different products, and Google offers many different products that it's trying to integrate into a single social network.
The reason for such opposing strategies is that the problems, constraints and opportunities for each company are completely different.
Why Facebook is turning one into many
Facebook started out as a single product. By this time next year, Facebook may total more than a dozen products.
Already, Facebook has spun out Messenger, which provides simple messaging; Camera, an alternative to your camera's photo app; Poke, a Snapchat-like app; and Home, which updates the main interface for some Android phones with additional messaging and photo options. Facebook also acquired Instagram, which is kept as a separate product.
Facebook is also expected to launch in the next week a new product called "Paper" (and internally code-named as "Project Reader"), which has been described as a Flipboard-like news reading app or web site (or both).
Facebook CEO Mark Zuckerberg has hinted at more separate products coming soon.
Another departure from keeping everything inside Facebook.com is the extension of Facebook ads to non-Facebook apps. The company said this week that it's testing the use of Facebooks ad infrastructure, sales features and social signals to deliver targeted ads on apps that are not otherwise associated with Facebook.
The idea is that ads would appear on ad-supported apps without being identified as coming from the Facebook ad network. But the ads would theoretically be more relevant to users, because each user's Facebook profile would affect the choice of advertising content.
From a user point of view, these ads are not a "product." But for advertisers, they are.
So why does Facebook want to turn its one social network product into many social products?
The answer is that Facebook is faced with a constant bleeding of users who are overwhelmed by the noise and complexity of Facebook.com. Or, users leave because they feel overexposed by Facebook's hyper-sharing, crowded social environment.
When users leave Facebook, they usually go to single-purpose sites, such as Snapchat, Instagram or Tumblr, or even a messaging app. They do that because they feel more in control of their "social graphs," as Facebook calls them, and their sharing. Single-purpose apps feel intimate.
So Facebook no doubt wants to give people single-purpose social apps to flee to. That's why they spun out Messenger, created Poke and acquired Instagram. Because if people are going to move to single-purpose social services, at least they can be Facebook's.
Facebook also wants "shelf space." One of the reasons retail products often come in boxes that are too big for the product is that companies want to take up as much space in the store as possible so the customer notices the product. Facebook no doubt wants mobile users to have lots of Facebook apps to maintain mindshare.
Why Google is turning many into one
Google, on the other hand, has a very different set of challenges. Google has long been in the "everything" business, from search engines, cloud email services and blogging services to self-driving cars and smart contact lenses.
Google is really in the business of big data. They specialize in making sense of massive data sets. Even simple acts like searching for a good slice of pizza on Google Search lights up supercomputers marshaling data like location, search history, the preferences of friends, and map data that includes real-time traffic information.
The more data Google can throw at every user experience, the better that experience can be and the harder it is for competitors to duplicate that experience.
So Google's aggressive "integration" of Google services into Google+, and integration of Google+ into other Google services, is really about moving toward a world in which Google has more user data available to optimize every interaction.
These integrations are really about adding a colossal set of social data, as well as identity data, to every possible Google site.
Google is building a set of online services that will make it feel like you have an invisible entourage guiding and helping and protecting you all day. It will be like you have a concierge, personal secretary, staff of researchers and other helpers with you wherever you go. Oh, and a driver, too. This entourage effect is being created with Google Now, but also many other Google products.
If you had such an entourage of helpers, they would need to know who your spouse, family and friends are -- who to let in and who to keep out. They would know your preferences and interests, and would help you pursue them. That's what Google+ and the so-called Google social layer is all about: letting your entourage know all about the people in your life so they can help you better.
So it's not really about unifying everything with Google+, but about integrating powerful social and identity data into the mix of behavioral, temporal, location and other data to make everything more relevant and tailored to every situation you find yourself in.
That's why Google recently killed off Latitude and the Android Gallery app in favor of Google+ or Google+-centric alternatives. It's why they built Zagat into Google+ and aggressively integrated Google+ with Gmail and YouTube.
It appears to be all about making all "signals" or points of user data available to any Google product in order to improve that product in ways that other companies cannot.
Zeroing in on advertising, which is after all the main business of both Facebook and Google, the outcomes of each company are more or less the same place. Each company is trying to attract the maximum number of eyeballs and serve up extremely relevant, highly personalized ads on both desktop and mobile.
In order to be all things to all people, each needs lots of services, products and apps, but all tied together with each company's social signals and identity.
To achieve this, Facebook needs a lot more products and a lot more "artificial intelligence," which are initiatives the company has explicitly said they'll take.
Google needs to take the many products it's already got and make them a lot more connected to its social and identity information.
So although each company appears to be headed in the opposite direction, they're really competing for the same destination: To add social intelligence to everything you do, plus add identity to everything you do so they know who they're servicing up ads to, while also enabling purchases.
Some day, Facebook might need to stop selling ads on the Facebook.com site altogether in order to compete against Google's ad-free social network. Sure, they'll still harvest social signals from the site, but they'll need a lot more apps for displaying advertising.
The question for Facebook is: Can it launch those apps and get people to use them fast enough to keep users and advertisers from wandering off to the next shiny new thing?
And the question for Google is: Can it integrate its social and identity layers to existing products without freaking people out and making them feel coerced and abused?
So far, Google is doing much better than Facebook, with far more users overall (Search, Google+, YouTube, Gmail and other services combined) and also a social network that's growing fast. Google is also way ahead in the algorithm and "artificial intelligence" department, and in the mobile advertising business.
Still, don't count out Facebook yet. It's still got the biggest social network, and its strategy of building or acquiring many new apps is the right one.
Facebook and Google are headed in opposite directions to arrive at the same destination. Whether either company can get there is anybody's guess.
This article, " Why Facebook and Google+ Are Headed in Opposite Directions," was originally published on Computerworld.com.
Mike Elgan writes about technology and tech culture. You can contact Mike and learn more about him on Google+. You can also see more articles by Mike Elgan on Computerworld.com.
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