Whereas the Polish strongly identified with the Catholic Church. It was not considered either a threat or a foreign religion.
Also we all know about the little thing called the Russian revolution. But there were many who at risk of their life continued worship after that time. I have many stories--both beautiful and heartbreaking. Of icons hidden deep and far away-- but within reach to be viewed for brief moments of prayer and worship. Many silent believers in those day.
I visited Russia back in the 1990s to see a friend who worked there. She said, during the communist days, people would put their family icon on the inside of their front door. That way, if police came through the open door, looking for evidence, it was concealed right behind them.
Also, some families’ icons had gotten completely darkened by generations of candles burning in front of them. The people could then claim ignorance that it was an icon and say, “I don’t know what that is.”