Why should they? The Democrats are neoliberals, they are not your friend. They are not going to do anything for you.
The American two-party system is designed in such a way that as long as the Republicans are overtly evil, the Democrats get a free pass to do whatever they want so long as they do not cross that threshold.
It’s designed to punish voters who think they can opt out of the electoral system by not voting. Don’t want to vote? You get the worse choice of the two!
And what the people are advocating here (not voting Biden) is exactly the behavior that the system is designed to punish. It’s meant to demoralize and break your will until you are no longer capable of resisting. It’s designed for you to lose.
The only way out of this is to have a political movement that does not play by the rules of the electoral system. But since such a movement does not exist in America, the least you can do right now is to slow the erosion of minority rights.
It’s the choice between evil and a worse evil. Or rather, Build Back Fascism Better or Make Fascism Great Again. And you will have made your choice between the two even when you don’t vote.