You're exactly correctlike when the default is to have children (which still is), and i'm asked about *my* children and i say: i have none.
that's caused strange reactions in some people, from pitiful to openly hostile.
and it's not that i volunteer this information. it's a question i can't just ignore without being outright impolite.
that compared to the question about a person's sexuality, which might not be asked that often.
or maybe it's a new trend?
You're experiencing the effects of differing from the social norm
It really isn't just asking about someone's sexuality, its things like asking if they're married or plan to have kids. Maybe they're gay and can't legally marry in their area? These and other questions tend to get at that core information by assuming everyone meets the default