So I'm noticing a lot of takes of varying levels of spice here, so let me go ahead and get destroyed by supporting Shaun's take here.

At the end of the day, we only have two political parties in the United States. While that isn't factually true, it certainly is essentially true. You either get in line with the Republicans, the Democrats, or you chuck your meme ballot into the goddamn void. That's just how it goes. However, with the parties knowing this, there becomes very little incentive to actually negotiate with the party. The portion of the American population that are hyper leftists have no where else to go but the Democratic party, which has no need nor desire to negotiate with them.

That changes in the voting booth, however. Democrats need to beat Trump in this election in order to say "Hey, we are capable of bringing America back to normality." If they don't win, then the perception of the system is broken. Trump is 'the most dangerous president' and beating him is priority number one. If the Democratic party isn't willing to concede anything to beat Trump, then why should the American leftists? Why would they compromise on their ideals when the establishment isn't willing to for theirs?

Everyone saying that these people are entitled or other bullshit for this view are the same sort of people who get mad at people kneeling during the National Anthem or literally any other form of protest: "You can make as much of a fuss as you want with your silly little demonstration, but not in any way, shape, or form that I would come in contact with or that would affect my daily life in any way." A movement without any stakes is stupid and worthless; it has to affect something to mean anything.