Well, I guess some of them (not all of them, mind you) would not be able to have similar income and quality of life at home as they have in Poland, working as native-speaking English teachers for example.
Indeed - any good teacher with half a brain can easily have a much higher standard of living here than in the UK. Of course, the good times won't last forever, but for now - anyone who is smart enough to save money and then reinvest it are the ones succeeding here.
Equally so, there are teachers who work all year, only to blow their savings on flying back home for the summer/winter. They tend to be bitter, resorting to posting anonymously on internet forums to complain about the country - yet their posts betray exactly what's wrong with them - they have a rubbish standard of living in Poland (because of the need to save to go home in summer) and see other expats and Poles enjoying a much better life.
Some of them just fell in love with the country and people and decided to stay.
Even in my case - I can drive from Poznan to the Czech Republic in about 4.5 hours maximum. Could I do that in the UK? Hell no.
Some of them are highly qualified specialists that are needed
in Poland at the moment and, consequently, earn enough not to think about leaving.
Ties back in with what I said above about certain teachers - they aren't qualified enough to succeed in Poland (because ESL teaching, long term, requires investment in qualifications, money that they spend elsewhere) in terms of getting a good, stable job. But the ones that do invest in themselves are the ones doing well - and these are the ones not eating Polish food every day!
If I, in fact, were someone who couldn't afford to eat in restuarants, I'd be offended.
You said, clear as day, that you eat Polish food everyday and that ethnic restaurants are too expensive. Anyway, you already posted all over Dave's ESL that you can't afford to even own a car here, so it's all coming rather clear, isn't it?