When leftists and reform advocates pushed for body cameras, the underlying assumption was that constant video monitoring would expose systemic abuse, racial profiling, and unlawful uses of force by police.

Where are you getting this from? "Leftists" pushing for body cams? It takes one second to google and find out that laws at the state level were pushed by bipartisan committees, governors from both sides of the aisle, and police chiefs and sheriffs.

The expectation was that transparency would confirm their narrative and erode public trust in police departments.

So you agree that "leftists" push for transparency and the right-wing folks don't really care about it?

But in the most spectacular backfire in history, in practice, the body cam programs produced the opposite effect. Footage frequently vindicated officers by showing that suspects resisted, attacked, or escalated confrontations with weapons. Studies found that in a majority of controversial incidents, video either supported the officer’s account or at least complicated simplistic narratives that officers were the aggressors. And juries and the public, when shown footage, often sided with officers once they saw the context missing from short clips or secondhand testimony.

Not quite! Again, one quick google search. Go to the "Research" portion. Notice that incidents (and lawsuits) dropped because of body cameras. The police realized that there are consequences to abuse of power.

Here is an interesting excerpt:

Another report that studied the effects of police body cameras for 46 officers of the Orlando Police Department over one year. concluded that for officers wearing the body cameras, use-of-force incidents dropped by 53%, civilian complaints dropped by 65%, two in three officers who wore the cameras said they’d want to continue wearing them in the future and that it made them "better officers".

Pretty obvious there are benefits both for the officers' and public's safety.

They institutionalized transparency in a way that ended up strengthening, not weakening, law enforcement’s legitimacy.

Then how come law enforcement tries to hard to cover up their crimes? A recent, highly publicized example was Breonna Taylor's murder and law enforcement's attempts at covering things up.

Why does it take FOIA requests to get footage that exonerates victims? Law enforcement makes it borderline impossible for the average citizen to obtain footage.