It's not the DNC's fault Bullock didn't qualify. He took until the last minute to announce, and his appeal is already taken by Biden, O'Rourke, etc.
I'm fine with that argument for a later debate, but all candidates with a real campaign (IE, not the people who are just unknown names on the ballot for the lulz) should get a chance to make their appeal to the people on the national debate stage.
A three-night debate with 8 slots each could have sufficed, and the next debate could have had a stricter standard.
The whole reason we have so many randos running is because they thought they could be one of the 20 who made the debate stage. If they had set the initial cap at 24 candidates we'd have 29 running