This is an extremely common trope from establishment Democrats who like to pretend the left is just naive children. Let me make this perfectly clear to you. Yes, we get politics. Yes, we understand that Biden can’t get everything he wants. Yes, we get that Republican obstruction is a thing.
Now, here are some things for you to try and grasp. Most of the time, Biden and the Democratic establishment is leading the opposition against the left. The establishment also plays dirty to get their unpopular candidates past the primary, then blames the left when they lose in the general.
It’s not generally the politically active left that doesn’t vote blue. Most of us are well practiced at holding our noses at the ballot box. It’s normal non-political Americans who see no point in getting engaged when neither party even speaks to their problems.