It's that you can get much better pay in Poland. Especially for lower skill jobs, higher skill jobs are not that different. It's easy to get legal employment and residence. The countries are close culturally and linguistically. And, of course, Poland is better developed -- materially and societally -- so the quality of life is better too. I think that at this point Ukraine can provide as many workers / migrants as Poland can absorb. And Poland can absorb a lot -- after its own big wave of emigration farther to the West.