QUOTE(Text @ Wed 25th November 2009, 6:35pm)
![*](style_images/brack/post_snapback.gif)
It's because Facebook has taken the lead as the site which absorbs the most users, and because the media (especially television) keeps saying that it's the "cool thing to do" at the moment.
Another reason: editing is still as easy as it was years ago, but cooperation has become much more difficult. Since hobbies are supposed to be a relaxing thing to pass time, and should not make people angry, many prefer going to Facebook and play crappy flash games to have fun.
I don't play the games, but I have left wiki as my primary site I lurk on for FB, so you're right for me at least. I like to mingle and most of the atmosphere at WP is mainly against people making friends/chatting etc. So it wasn't an efficient use of my time. (for believers in WP it might seem unlikely that FB is a more efficient use of someone's time I know lol, but if you like to make friends with people/chat, it is. The people on WP tend to be more reserved.)