It did some good things, absolutely. It got the cops charged, it showed people that direct action can move the ball forward where going through proper channels has failed (tearing down statues), it moved a lot of once-radical race and class discussions much closer to the political mainstream, etc.

But compare the material value of that to the cost people paid in time, effort, bail money, criminal records, and getting beaten by the police. How many people are going to sign up for that trade again? Isn't it telling that there's been no structural change, cops keep killing black people in egregious ways, and yet we haven't seen protests anywhere near the scale of last summer's? There are plenty of other factors in play (tons of people are still naively giving Biden a chance, or less-naively exploring local efforts that don't center on protests), but it's also rational to conclude that the cost-benefit of the BLM protests shows it's not a winning strategy (at least not right now). People don't want to invest in failed efforts, and if we're even half as skeptical of direct action as we are of elctoralism, we'd call the BLM protests a failed effort.

Note also that you can come up with a list of modest wins accomplished by the Democratic Party, too. People aren't going to look only at the good things done by protests and ignore the costs, but then flip that around when they consider the value of elections.