In 2020, people believed they were voting for healthcare, defunding the police, emptying the migrant concentration camps, protecting Roe v Wade, etc.
When you fail to do the things that brought people to the polls, and do the things the opposition wants instead, the opposition's voters still won't vote for you and your own voters just don't vote.
Trying to appeal to moderate republicans just lowers your own voter turnout. The republicans will always vote for fascism over diet-fascism.
But no, pointing out these very obvious mechanisms just gets me labeled as an evil conservative Chinese Putin-bot trying to disrupt the election.
dropping out of the race at the convention
The face of the party is infinitely less important than the impact the policies have on people's lives. It doesn't matter if it's Biden or Pete Buttigeig at the front, the dems only shot in hell is to use every power at their disposal short of drone striking Trump and the SCOTUS (maybe) to demonstrate to voters that 1. They want the same thing the voters want (eg, not genocide) and 2. They will actually do those things (no blaming the parliamentarian or norms or some rules you set or fear the SCOTUS might ask you to stop).