I still want to know why these people care at all.

Personally, I don't even want to think about the genitals of 99% of the people that I've met. I honestly don't want to know, it has nothing to do with me. I'm more than OK leaving some things unsaid. I don't want to know. If you tell me your own gender or preferred name, cool, I'll respect that and leave it at that.

Why do these people care so much about complete stranger's genitals? It is an obsession or a fetish? Is it just xenophobia?

The thought never even crosses my mind. I would be super grossed out if a stranger ever asked about mine, tbh. It's weird shit to judge an entire human off of, if you ask me.

If a strangers bits are important to you, you should really look into why that is.