I find that talking about them usually leads to a predictable surface-level conversation that I'm bound to find boring.
Usually it's only with other experts that I can have an interesting conversation about the details of something I'm very familiar with.
It has nothing to do with what I find most interesting to talk about. It has to do with me assuming that this is what you want to talk about, since you asked about it.
I also kind of expect the person I talk to make own pronouncements about the topic they started, without having to ask "what about you". When I am asking "what about you", it is usually admission that this is not going well, conversation feels one sided and I am desperately trying to make it two sided so I am not the asshole there.
Nor does what I said imply your assertion.
It follows that whenever someone has an obsession, it comes up naturally while they talk about themselves.