Why do so many Polish people leave Poland to work in other/live in other EU countries?

Do you know history? Have you ever heard about one ugly thing named communism? It destroyed Polish economy and produced a lot of corruption. Current Polish government is not doing much to improve things. Everything is better than ten years ago but it's still far from perfect. There is still quite high unemployment. Western European countries developed good economies thanks to capitalism and free market. That's why living conditions in the West are better than in post-communist countries. There are jobs for Polish people in many countries - England, Ireland, Germany. Poland is not as cold as you think. Winters are cold but summers are really hot.