Cuomo still got tons endorsements despite running as an independent against a Democrat, so it's not as simple as just party loyalism. There's a core of the Democratic party which hates socialism and socialists, and would rather lose than let socialism win. That's not rigging, though. That's just the party leadership (and donors) steering the party.

I fully expect a DSA candidate in 2028, so we'll see how the party reacts.