It was also one of the only country with the ability to confirm that the USA did go to the moon, and had every reason (politically) to call it a hoax and didn't.

That's why I still don't get moon landing conspiracy theories.

I accidentally got into a debate with a moon landing conspiracy theorist about this once. Their claim was that both space agencies were tacitly colluding to sponge budgets off of their respective governments. I dug into this further and after a couple of rounds of back-and-forth the answers they presented effectively required the entire Soviet political and ideological system to be a sham. I pointed this out and commented that, if true, this would be a conspiracy theory that makes a bit of NASA trickery pale to insignificance in comparison, and never heard from them again. I’d like to think they changed their mind, but I don’t think it's likely.

My (uncharitable) explanation is that it gives a comforting sense of control and understanding of the world to be part of an in-group that has simple explanations for every outsider’s (potentially complicated and technical) objections.