I'll be the last person to say that both sides same bullshit, but Democrats are still politicians. They seek positions of influence and power, and they need public support to do it. There's a certain type of person who thrives in that environment, and they are absolutely the last type of person you want in leadership roles.
Anyone who is currently in power will oppose ranked choice voting because it breaks up the monolithic power structure that so many powerful people use as leverage. It reduces the effectiveness of wedge issues, which means leaders will actually have to present nuanced opinions on many topics. It decreases extremism, which means their opponents will likely be closer ideologically to themselves, all of which is better for the voters and worse for the politicians.
Democrats in power love that the GOP has become unhinged. It makes the rational choice incredibly easy. Ranked choice will break up both parties into smaller categories, killing the demon they would rather be fighting.