I'm not an expert on the subject but my parents grew up in USSR and I've talked to them about this in the past. My father told me that back then, nobody was religious. Only old people went to church and the government didn't bother them. If you wanted a career, being seen in church was pretty bad.

I think that the religion was communism. They had a pretty conservative worldview. So when the system fell apart a lot of people needed a belief system to replace communism and turned to religion.

My dad like to tell the story of how they were painting a church basement with his friend one time to help out and they ended up getting drunk in there. The friend he did it with is now very religious, the kind of person you can't say "on my god" in front of without them screaming blasphemy. The effect was probably exaggerated by the fact this friend I'm talking about immigrated to Canada and religion probably started as a community thing, but I still think the same thing happened in Russia. The country changed really fast and people needed something to cling on to.