Maybe because those of us with plans and ambitions and successes don't want to seem like we're showing off to everyone.
Also as said above, it can be very hard for us, this place seems to attract people that struggle to get by elsewhere, more so than many others even on the internet, I have been for years pretty much incapable of getting a job because I couldn't even go into a shop and ask about a vacancy or anything, I still can't but come summer I am going to try until I can.
Besides, it's a lot easier to sit around doing nothing, especially if you have others to do it all for you, and those few people that actually care enough to go and achieve something, how many hang around sites like this all day?
I think my problem, though, is that I have too many ambitions, I can't put enough time, money and effort into achieving them all and I can't choose which one to focus on the most. Also, I'm kind of lazy, and like a few other people here I severely lacked social interaction until I found this place, and now I have the chance, I'm enjoying it, and it's taking up a lot of my time.