3 major european powers tried their best to delegitimize PLC for over a century so probably a lot of negative stereotypes can be traced to their propaganda and diplomatic efforts during partitions.
Then Allies sold us off to Stalin and it was rather inconvenient to hold a positive opinion about us. Afterwards Poland unwillingly became an enemy and a commie shithole which bred even more stereotypes (some unfortunately true for their time but it's easy to look down on others when you've rebuilt your country with Marshall Plan money).
Now we're baddies because we don't let towelheads rape and pillage.
Also it's apparently easier to blame us for the holocaust than to reeducate some morons who didn't get that 'Polish concentration camp' means 'concentration camps that were located within occupied Poland'. We need to exhume Home Army soldiers and wire their rotating bodies to a bunch of generators. We could power the entire world.