For same money, tourists prefer by very far to visit Croatia
Yup, pretty much. It's quite surreal that people spend the same money going to the Baltic Sea in summer with the unpredictable weather and freezing sea as they would on going to Croatia. I was looking last summer - I had a very nice, decent-sized apartment next to the beach for 30 Euro/night in Croatia. In Poland, the same thing was coming in at around 50 Euro/night. No brainer.
It makes me laugh that people think they're eating fresh fish on the Polish coast. One look at the fish and you can see that it's anything but ;)
Hotels are often disappointing, and when you go on holiday in Poland, there's often not very much to do.
Some places are quite ok, such as Karkonosze, but you're right - the infrastructure just isn't that developed. I did a summer camp in Darlowo one summer with a friend for a laugh, and it was striking just how little there actually was to do in the town.
Poland could do a lot more to encourage internal tourism.
Problem is, they've already wrecked many pleasant places through uncontrolled development. I remember being completely bewildered in Bieszczady that they could allow the night silence to be destroyed after 10pm with bars playing thunderously loud music - it really destroyed the entire atmosphere of the place.