Biden stepping down would create such chaos that it would guarantee Trump wins the election.
-Biden loyalists (both insiders and voters) will feel betrayed by the party for running the sitting President off and will say fukk it.
-If VP Harris isn't the nominee, black liberal women would be ready to burn down the party.
-Many people correctly believe Harris cannot win a national election, therefore they would try to get Newsom or Whitmer which would hurt Harris's position.
Harris cannot win a national election, and whoever is the nominee would have a fractured voter base full of hurt feelings and anger, no unity, and a diminished anti-Trump coalition.