Yes, in part, and also because the party is actively trying to prevent those voters from getting the progressive candidates they want. It's more blatant these days (Bush, Bowman, Mamdani) than it has been in the past, but it was still happening. They don't want pressure from the left. They broke their promise to not support primary opponents (over incumbents) specifically when progressives started gaining ground. Many are openly hesitant to endorse Mamdani now if they aren't openly skeptical or critical. Vote blue no matter who, eh?

More specially, people don't vote in primaries or local elections.