I'm guessing a combination of several places:

1. A lot of those people with $200 burning a hole in their pocket that will bust out quickly aren't exactly the type who are thinking, "Boy, I'd better stick to the 10NL game since that's all my bankroll will support." A lot will be just as likely to try 5/10 as .05/.10 just because they have no concept of bankroll management and they think that they're experts because they've watched the WSOP on TV.

2. There are rich people out there who just have money to burn. You may have started at .05/.10 with a $100 bankroll, but your average multi-millionaire is going to waste his time with that. Of course their play will be every bit as bad as the newbies at the small stakes and they'll get eaten alive by the sharks at the higher levels. That doesn't mean they'll hesitate to redeposit and try again though.

3. People are playing above what their bankroll allows. Some guy who plays regularly at $1/$2 decides to "take a shot" and finds himself horribly outmatched. Just because someone's playing $5/$10, doesn't mean they've really demonstrated the skill to win there.

4. Sort of related to the previous item, but most people, even solid players, reach a point where they simply don't have the skill to beat the next level. Not everyone that is crushing the .05/.10 game is going to eventually be a winner at 10/20. At some point they're going to move up to a level that they can't beat, lose some money, and drop back down. They'll make their money back at the lower level, take another shot, and lose again. Figure this happens many times before they finally get the hint and then multiply this effect by all the players out there and you'll see a "trickle-up" effect where money that is won by good players at lower stakes is lost at the higher stakes when they try to move up.