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.
They're basically a lib PR group that misleads people about what BLM is. The damage is the same as lib misinformation in general: difficulties reaching people with the message of radicalization, people going down a lib pipeline rather than socialist pipeline, having to explain why you're not responsible for the things done by the lib recuperation effort.