Bernd 09/13/2017 (Wed) 21:49:16 No. 10382 del
Few reasons:

First, sitting in complete isolation wasn't good for USSR. Even modern North Korea isn't fully isolated, and USSR was much more "liberal", especially in late period. So, they choose some popular movies and allowed them to be shown in cinemas. Why these? They were French, and France was "evil West but not so evil, even not in proper NATO". France and Italy also had strong commie parties, so it was a plus. These movies also were relatively mild in terms of western way of life, not like drugs-n-killings-n-shit.

Second, some movies gone into cinemas because people like Brezhnev loved them. There were multiple stories like when censors said strong no, but Brezhnev loved that movie and said "just run it".

You also must remember that not everyone in censorship community was a believer in glorious commie future, some people tried to fit movies they like into concepts like "it shows west in laughable way" or "it shows struggle of common man" etc.