I haven't been to Poland but have a second home in Czech Republic (my wife's country) which has the same phenomenon. It has nothing to do with economics or poverty and everything to do with people. Young people move to where the jobs are which means the larger towns and cities (this happens worldwide BTW). This means old villages are entirely inhabited by old people, most of whom only worked during the days of communism. They can't and won't change. They don't want to renovate or live in a new house. So the village gets run down. Canada (where I was born) also has run down towns and even ghost-towns, you'll just never see them. In Europe secondary highways pass through every town it seems, so you do see them.

My wife's grandma, now in her 90's, lives in a >100 year old farmhouse that's crumbling and only 1/3 of the home is even heated. Hell installing the electric heaters and indoor toilet involved a ton of arm-twisting. She's been insisting she'll die any day for the last decade and refuses to move or renovate. Meanwhile my wife's cousin lives in the same town (is a remote worker) and lives in a super-modern new home that's built to a much higher standard than the average new home in Canada. Old people are just stubborn...

Anyhow the point is that things only get renovated when the owner wants to renovate it, it has nothing to do with wealth. In the city, land is worth $$$ so inevitably it gets bought and improved. In small towns, meh...