I think the 2020 election was the conservative wing of the party's backlash against the progressive wing. From the concerted effort to derail Bernie and Biden's nomination largely on the votes of red state democrats (irregularities aside), and the progressive messaging notwithstanding, Biden's win was the old guard asserting dominance. They knew they'd face Trump again and were planning to capitalize on all the space to their right flank from the beginning. The fact that that's created conditions for NeverTrumpers and Hillary campaign dead-enders to thrive is probably more a consequence than a driver imho.