It's a win-win: you absorb languages for free as a child, and you later get to enjoy art in its original unmutilated form.
Those regimes had a... less practical approach to economics, and maybe they didn't want the population to know western languages as well.
We also translate a lot of books, even though the profit margins aren't that big.
The main source of government-critical information during the Communist era were the radio transmitters (RFE, Czech broadcast of the BBC, Voice of America) which were hardest to stop. Those stations broadcast in Czech and Slovak. Anything that had to cross a physical customs point (movies, books) was heavily censored.
You call it a win win, government calls it "foreign influence"....
Dubbing movies becomes a problem when you are exposed to the actors’ original voice or the original audio track of movies because dubbing is a poor substitute. And hearing the same voice for different actors breaks immersion.