There’s at least one explanation that would lead to the same result, independent of communism: All of these countries were occupied for decades by a totalitaria

There’s at least one explanation that would lead to the same result, independent of communism: All of these countries were occupied for decades by a totalitarian government that was flying this flag. One is currently at war with the successor state. Still, almost all of these countries have policies in place that in the US would trigger an immediate “but that’s communism!” reaction - for example universal healthcare and social security. The underlying reasons for banning the USSR communist party flag is very likely to be much more complex than a single cause as you suggest.