I would like to understand the reason why any left-leaning progressive Americans would not vote for Biden (including not voting at all). Can someone explain?

Racism? I know tons of deeply racist liberals.

Ok, although I probably wouldn’t call them “left-leaning progressive”

I dunno. I know lots of racist and misogynist Bernie bros who all will talk your ear off about being democratic socialists. 🤷‍♀️ None of them plan to vote for Biden, and their main hobby is terrorizing women and POC who plan to vote Biden in November.