My friend webspelunker Ghostraven is meditating here on SL and whether or not it has fulfilled its promise.... Comparisons to Facebook crop up. (Let's not dwell on the fact that, if you bought into Facebook's IPO, you could legitimately question whether that has fulfilled its promise, either.)
Now, Web is not the only person I've seen making that comparison... and, frankly, I think it's what they call a category mistake. Why is SL not as accessible and popular as Facebook? Well, very simply, because they do different things. Comparing them is, then, a matter of apples and oranges. SL is not very good at doing the sort of things that Facebook does, because that's not what it's for. Conversely, of course, Facebook is absolutely lousy at doing the sort of things SL is good at.
The foundations of SL - I keep saying this - are creativity and socialization. Facebook, naturally, is great at the socializing thing. (So I'm told. I do have a Facebook account - under my real name. If anyone wants to find out who the "real me" is, they could try it by looking through Facebook accounts finding one with little to no activity. I log on, once in a while, find that one of my four friends has posted some link to a "photo of the day" that turns out to be a poorly disguised phishing app, and log out again.) The creativity, though, is effectively nil. Facebook is great for creating links to stuff that's been created - photos, products, poorly disguised phishing apps - but what tools does it have to make stuff inside Facebook itself?
SL, conversely, is all about the creativity. In the beginning, the regions were almost literally a blank canvas for people to draw on.... Today, there is enough user-generated content in SL to keep any sensible person (a category in which I do not include myself) occupied for years.... Even so, even if you never turn on the build editor, modify your shape, or make a new clothing item from scratch, you still have to have some creativity to operate in SL; you have to create, if you like, a narrative for yourself inside it - you have to decide how you are going to interact with this virtual world. This is a problem pretty much unique to SL; in an ordinary MMORPG, you have a narrative role which is - within some scope for variation - pretty much laid out for you. The problem of finding or making your role in SL is a key one - the question "What do I do next?" is probably the one I see most often at Oxbridge (all right, after "wan 2 f**k?"). And failure to answer that question is probably the biggest single reason people stop coming back. It's not an easy question to answer. It takes thinking, and thinking's hard.
This is, in fact, a key reason why SL isn't as popular as Facebook, and in all likelihood never will be. It's not a question of barriers to entry - it is not noticeably harder to sign up for SL than it is to sign up for Facebook - it's a question of barriers to engagement. There are a lot of simple, obvious, well-signposted things to do in Facebook. You sign in to SL, though, and there are no signposts. You're on your own, and you have to figure out for yourself what to do.
And, of course, getting there is a lot tougher. If you are a social animal, finding a congenial group and gaining acceptance is hard work in itself. If you are a tourist, you will trudge across an awful lot of blank green land and abandoned shopping malls before you find a destination of interest. And if you are the creative type, learning to script and build and make clothing textures and mesh shapes... it's a whole career in itself.
(Am I putting down Facebook users here? No, not really. I doubt Facebookers are any less creative or intelligent on average as SL people - but they do choose to spend their intelligence and creativity on stuff outside Facebook itself, because creating on Facebook just isn't an option.)
So... SL is less popular than Facebook, because it is more like hard work, and that hard work isn't going to appeal to everyone. I think of it this way; Facebook is a sort of combination of desk jotter and photo album and bulletin board... SL is a creative medium. Using Facebook, therefore, is like writing in a desk diary; using SL is like writing a novel. There is nothing intrinsically better about either activity (unless you are Jeffrey Archer, in which case please stick to the desk diary), but one of them is harder work, and has a more specialized appeal. So guess which one is less popular?
I suppose it comes back to the "hype curve", as Tali keeps pointing out. SL has reached a point where people are stopping being disillusioned with it for not living up to the hype... it remains, now, to use it for what it does do well. Whatever that may be!