Not only do human beings have to monitor the surveillance technology, but there will always be cost considerations that leave some places in the facility without video coverage.
Staff members who are up to no good will soon find out where those are, and that's where the abuse will happen.
Also, the humans who monitor the video can be bribed, or they can become the instigators, because the watchers will have a lot of power over those they are watching.
This happens all the time in prison settings. There is lots of surveillance technology, but bad things still happen all the time.
I don't think there are enough high-character people to hire to staff institutions that have it as their mission to take care of people who (1) can't take care of themselves, and also (2) actively resist being taken care of by others. I'm afraid this is just an irreducible fact, at least for now.
Conceivably, robotic attendants might handle the problem someday, but it will be quite a while before that happens.
And that doesn't even touch on the problem of actual criminals who pretend to be insane, find a place within asylums that are intended for people who are really insane and helpless, and then proceed to abuse and exploit the helpless residents. It only takes one or two of those cases to taint the entire institution in the eyes of the activist media, that will turn such incidents into opportunities to advance the political agenda.
Well said.