It follows that whenever someone has an obsession, it comes up naturally while they talk about themselves.
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.
I am not convinced that this is true. I think a lot more people are really interested or passionate about something than you may realize, but not all of them talk about those things to everyone. Alternatively, their passion might be what they do for a living.
So for instance a case of the former might be someone that has a very niche interest, so they have learned that in most cases talking about that thing does not lead to any interesting conversations.
Another possibility is that they might not view themselves as being particularly good at their area of interest (which may or may not be the case), so they don’t like to talk about it.
So for whatever reason, including the above or other reasons, you end up not learning about these interests that those people have when you just talk casually with them.
And as for the people that do it for a living, it could be that they have no interests outside of work, because work fulfills their passion. For example someone who is a really passionate salesperson, if they already truly derive meaning and joy from doing what they do at work, maybe they don’t need anything outside of work other than to relax and recover.
Lastly, another group of people I can think of are those that have interests that are very costly and they don’t have a high paying job. So most of the year they spend a lot of time at work and on the spare time they sit in front of the TV, or the computer and it sounds like they have no passion for anything but really they are spending a lot of time dreaming about the next trip they can afford to go on in the Himalayas or whatever, and when they sit at home they watch programs about skiing, and they read about skiing online and discuss it with others online, and maybe read magazines about it as well.
I’m not saying that everyone has something that they are deeply interested in, but I believe that more people do than one might realize.