I feel like a good chunk of it is that Poland was hit with by the first decisive punch thrown in WW2 so it isn’t remembered as powerful like other European nations involved in WW2… which leads people to be surprised when Poland appears to become a major power “out of nowhere.”

People readily assume Germany is the European military industrial heavyweight in Europe because of the stereotype of Germany as powerful while not factoring in the fact that any country hit first in the outbreak of a world war such as WW2 is going to be taken out of the fight if there isn’t an immediate international response. Poland was and is an industrial powerhouse, if that is surprising to people I think that is because people are lazy about their stereotypes.

Poland made the fourth-largest troop contribution in Europe,[124][125][126] and its troops served both the exiled government in the west and Soviet leadership in the east. Polish troops played an important role in the Normandy, Italian, North African Campaigns and Netherlands and are particularly remembered for the Battle of Britain and Battle of Monte Cassino.[127][128] Polish intelligence operatives proved extremely valuable to the Allies, providing much of the intelligence from Europe and beyond,[129] Polish code breakers were responsible for cracking the Enigma cipher and Polish scientists participating in the Manhattan Project were co-creators of the American atomic bomb. In the east, the Soviet-backed Polish 1st Army distinguished itself in the battles for Warsaw and Berlin.[122]

https://en.wikipedia.org/wiki/Poland