i think--and maybe less than it used to be, you've cited a lot of reasons where this wouldn't matter--but in think in part because a lot of the "childless-not-by-choice" demographic is queer.
like. Yeah my partner is not down to raise kids with me and I got disabled by long covid, but even aside from and before that, I, as a big old lesbo, did not have a dude I felt comfortable asking for an old-fashioned sperm donation, and did not have the money to go to a sperm bank. It costs a fair amount of money to get knocked up if you're not doing it the traditional way! And if you're a gay guy who wants to hire a surrogate I imagine that's expensive and complicated too! And if you're not set on being biologically related to your kid and would be happy to adopt--well. Adoption agencies tend not to be super great about queer couples.
And I think that yeah there's a growing demographic of people with access to birth control and family planning who are barely scraping by saying "we can't afford to have kids," but also I think
people who have sex with the opposite sex (whether or not they're purely straight) can have accidents so much easier. And a lot of couples who end up accidentally pregnant might go "no we did the math this is impossible" but some of them go "we're gonna make this work somehow we want it too much."
and those kinds of accidents are much less common among queer people, so fewer of us get put in the position of "we said we couldn't but now I'm pregnant and I don't want to give it up, what now."
So overall the proportion of childless-not-by-choice people is much queerer than other segments of the population
and there's resistance to talking about it from both sides. Like. Homophobes don't want drag queens to read to kids at the library, let alone have and raise kids of their own, obviously. But on the flip side, there's a vein of queer culture that rejects the cultural norms of sort of, "cookie cutter" straightness. Like there's an idea that to come out and be properly queer you have to reject not only the idea of a traditional marriage to a partner you're not attracted to but also everything that goes with it, the picket fence and the 2.5 kids. So I think many queer people feel like if they talk about wanting kids, they'll be labeled as "too normie" or something.
I hope that'll change, that as same-sex marriage gets (and hopefully stays) legalized in more places, there will be more room for queers who want to raise families.
and i hope that all the other shit, the people who are getting worked to the bone and can't afford to take care of a kid even if they want to, I hope to see that particular societal ill get fixed in my lifetime.
And disability and mental health stuff--well case by case, everyone is different, but to be honest money would solve a lot for a whole lot of people.
but as to why don't we talk about it? Because no matter how common it's becoming, all of those things are related to marginalization. Whether it's queerness or disability or poverty--by and large, society does not like to admit we exist.