im just going to throw a theory out. i havent thought this through at all...
The Dems entire identity, and popularity, comes from a time when conservatives were conserving an actual bigoted culture. It is what made the left appealing, standing up against tyrants.
They dont seem to have actual stances on anything, aside from just taking the counter to the right. Their passion, the frenzy they whip up amongst their flock, all requires there to be an argument, and a ‘taking a brave stand against the bigoted bully’
As time has gone on, our culture, and even our conservatives have largely, by majority, agreed, “ok, women need to be given jobs and education. ok, i guess abortion. ok, blacks are Americans. ok, no more gay bashings”
All the fights have been won, on a consensus level. Taking the Trans side, making them the new focal point to stand your ground... the new hill to die on, is not all that is left (still guns and abortion terms to argue about), but it is one that I cant conceive of conservative-minded people bending over on. Trannies will always be the little guy that needs sticking up for by courageous progressives.
I dont think its an actual winning strategy (but I didnt think Trudeau would win re election) but i think, rather, it has just been drummed into the Left that the only thing that matters, their only true identity, is to oppose the Right.