It’s not that easy. You have to make it through the primaries to stand for election. Both parties are increasingly dominated by their outside wings. If you said “I’ll try to get universal healthcare done and I’ll build the coalition needed for it, even if it means accepting painful compromises like not covering gender affirming care” you won’t make it out of the democratic primaries. That’s why there’s so many common sense positions that have majority support yet never a majority in political bodies.

What I mean is that if the conservatives only objection to universal healthcare was these things, they could just leave them out. There's no requirement that a single payer system cover all procedures.

Ergo the reason they didn't support the ACA and won't do this is something other than it covering hormones and abortion.