This is the most charitable way of seeing it for them, honestly.

I think many of them don't actually have any interest in even incremental 'progress', at least not any more than it is incidental to their goal of gaining and retaining electoral power.

They abandon their 'progress' as soon as it becomes an electoral liability, and scold and police voters in their 'tent' for bringing up those issues when it isn't to the party's advantage. Anyone with moral or ethical principles (and are vocal about them) in the democratic voter base is liable to be pushed out as soon as it's no longer convenient to support their interests.