Simple — Biden steps down and there’s a free vote at the convention in July. This is so hard for you to understand only because you don’t want to understand.
The DNC is a private company. It constantly changes their own rules when it suits them, and have argued in court that they have every right to do so. Consider how they parachuted in Bloomberg, against all their rules, without any explanation, seemingly entirely to make Biden not the most right-wing candidate.
Your idea is that the DNC’s rules as they are this instant are a suicide pact — that no matter how terrible Biden, we have to stick with him, even though they have yet to actually be confirmed as the candidate!
No. The Democrats must win. Trump winning again is too awful to contemplate. Why you want Trump to win again by supporting a candidate who doesn’t even want to campaign is beyond me. It is my belief that you are so enraged at centrist candidates like Sanders and Warren that you’d far rather Trump won because he’s much closer to your politics.