It's a big country with large regions that are still comparatively poor and agricultural. The latter two factors are what the EU pays for and the first works as a multiplicator.
Per capita it looks a bit different. According bpd.de the main recipient per capita in 2022 was Estonia with 677 Euros per capita and year and the main contributor is indeed Germany with 237 Euros. Poland "only" gets 279 Euros per person and year.
Agriculture is a great point overlooked in this chart.
EU puts a lot of money into this, and Poland being a great exporter for this, they also receives alot from EU to be able to do this.
Why are we doing it then, if it's a net negative? It's not, because we can all get our bread (literally) this way. And Poland farmers can make a living making the country richer.
All countries get agricultural subsidies and Poland is not one of the big ones. They sit on place 5 with all 4 before them production at least twice as much. (see here, page 10)
None of the former Eastern Bloc countries are net contributors in this chart. Greece, Portugal, and Spain were also dictatorships not that long ago. Cyprus there's the whole Greek military Junta and Turkish invasion thing.
The only other net recipients are Malta (which doesn't receive much), and Luxemburg and Belgium. They host a lot of EU institutions.
Love the former East Germany, lived there for a while, but it's still deprived even after the federal state pumping loads of money into it. I suspect West Germany's crumbling infrastructure is in part caused by the burden of absorbing East Germany.
But it's not an independent country, so it's hidden in these figures. Germany's had to shoulder that burden on its own.
Cost trillions. West Germany shouldered that burden, but West German companies also profited from it. Eg. not as if there were private East German companies to build motorways to western standards.
PiS combine socialist economics with one-party control of state institutions, so while their rule has technically not been communist, it has rhymed with it.