But "the people" were on Myspace, Hi5, Friendster and other social networks before Facebook - hundreds of millions of them. So clearly it's something about the product, too.
That "something about the product" was that cooler people were on it. Facebook started with the ideal situation of seeding its initial users with the most exclusive club at Harvard. From there, it spread to all of Harvard, then all of the Ivy League, then all elite colleges, then all colleges, then all college and high school students.
It's absolutely classist. I saw the research when it came out and found it quite interesting.
Thing is, class divisions are a fact of life. If your goal is to pursue a more just society, it's worth trying to minimize them (though even then, you need to acknowledge them before you can do anything productive). But if your goal is to get maximal user uptake for your new social network, it's worth exploiting them. They aren't going away, and if you don't, someone else will.
A lot of Web startups have actually had the byproduct of significantly lowering class divisions, eg. Google gives important information to people who would not otherwise have had it, Twitter lets people organize who would otherwise have been divided & conquered by oppressive regimes. But to get there, they need users, and one powerful way to get users is to be seen as a status symbol that makes one cooler than their peers.
Regardless of whether exploiting class divisions makes good sense for increasing product adoption, I'll reiterate that it was not class divisions that killed MySpace but bad product divisions.
MySpace's ad deal with Google encouraged a site design that was anti-user. Facebook developed their own ad platform that allowed them to extract value from data that only Facebook has and that third-party networks couldn't get value from because it's so specific (like where you went to university).
But as much as the movies would have you believe Facebook won on "coolness", it won on old-fashioned better product decisions.
While that's true, I don't think any of them really had critical mass. Of those you mentioned, I had precisely one friend on Myspace, none on Hi5 or Friendster. I had two friends on Orkut. I think Facebook played it smart by making it an exclusive network on college campuses at first, then opening it up.
I don't think the exclusivity was a long-term strategy, but rather a natural progression from its beginning as a site for Harvard undergrads. It was really useful at providing specific needs for college students at the start. It was easy to find who was in your classes so you could ask for homework help or invite people to work on a group project back when everybody listed their classes through Facebook's central app. But after it opened up to everybody and a whole bunch of apps appeared, there were multiple competing class-listing apps with no clear winner and you needed to use all of them if you wanted to see everybody in the class. It became less convenient and most students no longer bothered to list their classes at all.
Once Facebook understood the appeal the site had to the general population, they realized that it would be better for them to create an ecosystem where network effects were optimized for the decentralized user base as a whole rather than the centralized subnetworks that made the site take off in the first place. At each step, they focused on what worked for the users at the time.
Google+, on the other hand, really did deliberately start out as an exclusive network, largely for people in the tech world, and it hoped to quickly transform into something with universal appeal. You can draw your own conclusions about how well that worked.
Facebook played it smart and still plays it smart by devoting much of their user interface into coaxing you to engage non-users or infrequent users of the service. I would rather just see a news feed, but that UI only gets you a FriendFeed-size user base, not Facebook.
Except if you go backwards from Facebook, there was at least an order of magnitude fewer people on MySpace, at least an order of magnitude fewer than that on Hi5 or Friendster, and so forth. Facebook reached a critical mass that the others never did.
Facebook says they have 845,000,000 "active" users. log10 of 845,000,000 is 8.9 or so, log10 of 200,000,000 is 8.3, leaving about 0.6, or most of an order of magnitude. And Facebook hasn't peaked yet.
Interestingly enough, I see lots of people around me moving to WhatsApp, undermining FB's undermining of E-Mail. (My uneducated guess: because FB is absolutely TERRIBLE at mobile.) So nothing is cast in stone, it is just that G+ simply failed.
Google+ is only cool for geeks, if even that. I'm not sure what to do with Google+. The technical folks I work with aren't sure. The non-technical people barely know it exists.
