It’s because when they republicans criticize the democrats they either don’t make sense or they’re factually incorrect.
Republicans are also in no danger of having their mind changed. That’s sort of their whole thing.
They grew up with everyone being a man or a woman. Normal people are straight, but there’s also The Gays™, and that covers all human sexuality. If people are poor that’s their own fault. Unions are a waste of money and the government ought to mind its business. Let the market sort itself out. This is just the way things are, and trying to change things is stupid at best and only going to make things worse at worst.
Democrats, liberals, can have their minds changed. A lot of us used to be liberals.
We can get pretty frustrated sometimes, I admit. Cut us some slack, please, we have a lot to deal with. We actually do call out republicans as they come up with new takes that indicate a level of brainrot that would make the eponymous Army of Darkness blush, but it’s like trying to shame an earthquake or admonish an avalanche.
So we have them to deal with, and we have the latest out of touch blue tie-wearing fossil inhabiting the oval office. We have everyone that defends and enables him and people like him to continue unabated. We could just call this whole group “capitalists but with at least some scruples probably.”
On top of that, we have people in our own group to deal with. There’s nothing some leftists hate more than leftists. Have mercy on your soul if you state one opinion that someone disagrees with.
So when we get upset if, for example, someone says we don’t care about “X” because we refuse to vote for the latest blue raspberry flavored oligarch then it’s probably because we are a little on edge from having to put up with derision from everyone else on the planet all of the time.
At the end of the day we need more allies, and with criticism we hope that some small fraction of liberals will be made to question things and possibly maybe at least give some serious consideration to the idea that the current socioeconomic system isn’t entirely perfect.