I've known guys who go overseas and work for stints of 1-3 years. During that time, they like in really shitty, dangerous locations (like the Middle East), little contact with their family and not a lot to do but work. Why do they do it? Because the $$ is fantastic and mostly tax free. I put these girls in the same category, except they probably have to work a lot less hard. As I've said before, I know these girls and what their typical day is like. Some days only 1-2 customers and lots of free time to fritter away. Even those girls who say they would rather do something else keep coming back, over and over.
Some on this board call their jobs "soul killing". I won't dispute that, though some do seem to enjoy it. That may or may not be an illusion; only they really know. But real world jobs can be soul killing as well (there's lots of ways to kill a soul), exhausting, dangerous, and often not very well paid. Plus your share to the tax man. I'll submit that anytime you work for someone you despise, it's soul killing. I also know people who worked in factories for shit wages and lost fingers or worse.
As far as LE entanglements: yeah, it sucks. But unless these girls actually own the spa, they'll probably never do any jail time. If it gets really bad, they can just go to another city (under yet another assumed identity) or go back home. It all part of the opportunity cost. They make their decision and it's a rational one.