This isn't nationals. There's too many races here (every House seat and 33 Senate seats) for them to fight every progressive candidate. That's why you occasionally see them give up and endorse a few progressives here and there.

Also, most of their work is done in the primaries. They tend to just accept the D candidate once that is done and over with. That's what happened with Mamdmi. Mostly because that's honestly more important than the real election, and also because they kind of have to to keep the ruse up.