I don't think that's a spoiler, it's the same in previous Fallout games. The vaults often have some kind of weird social experiment going on, and they've fallen into anarchy over the centuries. You might find some that are still viable, but the people inside could have developed some weird cult, or something like that. In Fallout 3 it was forbidden for them to leave the vault. You never know quite what you're going to find inside, although most tend to be ruined.
There was a fantastic one in Fallout 3 where the residents were in suspended animation, living in a 1950s black and white virtual reality utopia. You could put on a headset and join them, and you had the choice of telling them the truth about the world or letting them live in blissful ignorance.
I think Fallout is my all-time favourite game universe. I love the whole post-apocalyptic thing in a lot of other fiction, but the 1950s aesthetic and the vaults make this really special. The Wool series of novels is quite similar (but not as good).