They already have. Sanders significantly changed his platform. Reforms in policing are being made around the country. People care about the issue. Even those critical of BLM admit there is a policing problem. That was not the case before BLM.It is a "how can we make sure #BLM affects meaningful change?" kind of concern.
I disagree. Sanders can attribute a lot of his success from the conversations OWS began. Shifting worldviews is as important, if not more so, than policy changes. Policy changes flow from ideas and ideas flow from worldview. As Milton Friedman said, "when you have a time of crisis what happens depends on what ideas are floating around, and what ideas have been developed, and thought through, and are made effective." Friedman was wildly successful at completely changing how we approach economic and moral questions. To our great shame, I might add.Occupy Wall Street grabbed headlines for a while, but ultimately didn't do much besides start conversations (which haven't lead to much until today).
Those movements made steady progress over long periods of time. How long did it take the Abolitionists to reach their goal? How long did it take civil rights advocates? Indeed, that work is still ongoing.Part of the issue might just be that not much time has passed, but mass movements in the past have been able to successfully agitate for change, so we know it is entirely possible.
First you have to change minds. Then you change policy.