There are a number of problems, all of them intentionally created.
You’ve got departments that don’t want well trained, intelligent candidates. They want snowflakes, they get snowflakes.
The job has gotten so risky, and not just because of the perps, that the kind of people you’d really like to have apply just won’t do it.
Then you’ve got the problem of departments that, for various bad reasons, are running older, more experienced officers, the ones less inclined to blindly follow illegal orders, out so they can be replaced with said snowflakes.
This is all being done deliberately with the goal down the road of federalizing the fuzz.
It's always been that way. There's a Raymond Chandler book from the 1940s that includes the line, “Police business is a hell of a problem. It’s a good deal like politics. It asks for the highest type of men, and there’s nothing in it to attract the highest type of men. So we have to work with what we get...”