Because “they” love power more than they love him (Cuomo).
And now they sense throwing him overboard is in their own best self interest.
“They” could be wrong, I don't know. Cuomo, like that governor in Virginia, has some cards to play. Maybe Cuomo can survive; after all, he is a Democrat in New York.
Cuomo's problem is that he is a bully thug even with his own party, Democrats have the long knives out and they are piling on in unimaginable fashion. They know Cuomo is toxic for the Dem ticket in 2022, that's the real reason, self preservation.