Poland had a population of around 3.5 million Jews before WW2, of those around 90% were wiped out by the Nazis. If it was as antisemitic as you seem to think it was, that population would have never grown so large.

Now unfortunately, right after one antisemitic regime was toppled, a second replaced it. The cult of Stalin, the Soviets. Communist Poland was a puppet state that was forced into carrying out Stalin’s policies, a lot of which were incredibly anti semitic. However that regime also eventually fell, leaving modern Poland to govern itself.

There isn’t a huge population of Jews anymore because of the tragedies during the 20th century, a lot of people don’t immigrate to Poland Jewish or not, so it’s not surprising the population hasn’t risen. People are far more likely to leave Poland instead