The Democratic coalition is reshaping itself into a very atheistic, militantly secular, rich party of white people who care deeply about "people of color." I put that in quotes because I have seen that particular phrase used so much in the past few weeks by progressives upset that someone like Joe Biden thinks he has a shot at being the Democrat nominee. Turns out, Biden thinks he is the guy to save the Democrats.
The reality is a large portion of the non-Trump voting public that does not identify expressly as progressives, are as leery of the progressive drift of the Democrats as they are the Trumpian GOP. Biden conveys himself as an adult in the room and, more importantly, not hostile to moderate voters or blue collar voters.
Suburban voters did not suddenly wake up and decide they were progressives. Republicans lost them because they wanted a check on Trump. They are not suddenly in favor of 70% tax rates, abortion on demand, men in their daughters' bathrooms, and declining standards of living to scratch an environmentalist itch. Biden seems positively reasonable to them.
He'll give the left good Supreme Courts, he'll push their preferred agendas, but he won't scare the suburbs.