Yes, and the rules were voted on by party members before the primary started. They’re now in place, and they’re obligated to respect them until this process plays out. Same thing happened in 2016. Say what you will about whether the rules were “fair” or not, they were agreed upon before Iowa, and they were respected through the Convention.

The way you use “kneecap progressives” tells me you’re conflating DNC primary rules and campaign finance. The two are not the same thing. They could do to Biden what they did to Bernie and blast the airwaves with damaging, misleading attacks, but none of that would fundamentally change the fact that the primary rules were agreed upon and are immutable until the Convention comes to a close.

And to reiterate, it’s not “principles” that are holding them back. It’s a contractual obligation whose violation would open them up to civil litigation. Voters picked delegates and they’re obligated to respect the voters who selected them. The DNC can’t just tell them to take a hike.

But Biden can.

edit: AP just put out a piece that confirms what I’ve been saying. They’d be sued into oblivion if they usurped the process right now. The ball is very much in Biden’s court.