Given a choice between being a care assistant cleaning up old people's shit and sick for £7.50 an hour, and having sex with people I don't find particularly attractive for £120 an hour, I know what I'd rather do. Eastern Europeans are, on the whole a lot more pragmatic than Brits because of all the bullshit they had to put up with at home.
Most of the jobs they come over here to do are really, really shit, boring, often dangerous, badly paid, and the locals can't be arsed to do them because they're rather bum around on the dole. So yeah, I'd say hooking is a pretty good gig compared to that.
I also suspect that it's less psychologically taxing being a prostitute in a foreign country. Most of the girls I've spoken to view their 'back home' lives as very separate from their 'uk' lives. There's certainly less hassle with trying to hide what you are up to from family, friends etc.