Because the serving industry is a huge job market in the US. I was at a random restaurant / diner having breakfast, which in the Netherlands would have maybe one or two serving personnel running around - wasn't particularly large, maybe 30-40 seats. They had five or six people running around.

I have to add though, the serving and attention to customers was much better than over here. You're frequently out of drink in restaurants/bars over here, and the serving personnel doesn't seem to have the time or will to take care of that. Which is a missed sale, of course; over the course of an evening out, that adds up to 1-2 lost drink sales.

And also because a lot of people just can't get a job in the area they want. I know of a lot of people online that went for a degree in game design, but the jobs just aren't there. If they do get a job in the game industry, it's often as tester - bottom of the ladder.