Dems successfully completed their main mission; take over left-wing movements (or at least groups with potential), take them over and turn them into "voteblue" movements, then destroy them. Sure, this isn't purely the doing of the DNC (some leaders of the BLM movement were killed by cops, some sold out, some walked away), but as soon as Trump became president - especially when he started to attack Kaepernick, this started to happen. Then on 2020 election day, Dems immediately started blaming the BLM/defund movement, even after they successfully turned it into a "vote blue no matter who" movement.
The national BLM org is a rag and shitty so this is 100% unsurprising. All real and impactful organizing is and has been at local levels. But even with all that, a chunk of the smaller local BLM groups have too much faith in the national org and listen to them too much or direct donations they could use to the hundred million dollar national group. It's fucked up