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.
Those regimes had a... less practical approach to economics, and maybe they didn't want the population to know western languages as well.