Biden's ground game sucked.
I remember reading articles months ago about how his outreach to Hispanic communities was almost nonexistent. (I think it was Julian Castro complaining about it, but not sure) His coattails didn't bring anybody along with him for the most part; Democrats lost ground in the House and probably won't have the Senate either. Biden didn't so much win as Trump lost because of his completely incompetent response to COVID-19 IMO - people voted for Biden because they were tired of Trump, but then went down and voted for their Republican Senators and Representatives.
(By the way, STOP FUCKING CALLING HER POCAHONTAS. Thanks for doing Trump's work for him. Hell, I thought I had Native American blood based on family oral tradition until my dad did 23 and me - turns out we don't, but we do have a drop or two of African American DNA, which may be why one of my extremely racist great aunts suddenly stopped doing her family tree research without explanation.)
Warren had a great grassroots network going. She had a lot of broad-base support from the left of the Democrats that unfortunately Sanders took when he showed up to poop on the primaries. Most of all, she wasn't afraid to fight against the Republicans, which is a big fucking weakness with Democrats these days. They're terrified somebody is going to call them a liberal or a socialist, and they run around with their tails between their legs hiding the fact that Moscow Mitch took their balls and keeps them in a jar on his desk.
This is the other side of the problem - the Republican party is FUCKING EVIL. Not "hey, these guys could be redeemable some day", no, they are literally willing to burn the country down if they're not the ones running it. Hell, they're willing to burn down the country even if they are running it.
Biden's going to go all "Oh hey, wouldn't it be nice if we were friends again?", the Republicans are going to cut his balls off and put them on Moscow Mitch's desk, and in two years HUGE red wave over manufactured Democratic incompetence. I hope I'm wrong, but *shrug*.