Given police officers are in fact a part of the same society as the people protesting against them, it seems likely that the issues with brutality, and racial prejudice, are not endemic to police themselves, but indicative of problems of the overall society at large.
If people are protesting the symptoms of these broader cultural issues, and not the underlying cause, it seems an inescapable conclusion that any change will largely be ineffectual.
I feel that the difficulty with this, is that noone likes to admit that there are systemic issues in the way their society functions. From a sociological perspective, most people don't want to be beating a drum that runs counter to popular opinion.
Similarly, most people are reluctant to engage in confrontation on an individual level, when encountering behaviour that ultimately leads to these type of outcomes.
Just as importantly, most people are awful at taking responsibility for their role in a problem. People prefer to create a false dichotomy, and position their impact on problems as meaningless, and view solutions as outside their locus of control.
This effectively leads to a kind of tragedy of the commons, where responsibility belongs to everyone and is taken by noone - similar to what we see with climate issues.
To effect meaningful change, it's usually required that both individuals and groups make their voice heard and actually do something. Yet most people go about their lives, and only take action when the collective does, in response to some climax of conditions. This is better than the inverse - of individuals taking action while groups do nothing - yet usually results in neglibile change, if any.
I suspect a part of the problem is that a sizable demographic cares, but only insofar as they care to signal their virtues. Yet when it comes to doing something themselves, the it's a much lower priority. I also suspect most people in this situation engage in a cognitive dissonance that's almost automatic too - and probably aren't even aware that they're doing it.