And cops get away with harassing people all the time. The US courts have been doing an abysmal job of protecting the citizenry from police abuse. (E.g. qualified immunity.)

The thing that has been to some extent reversing that trend is cheap and ubiquitous video cameras.

What if the body cam happened to be off, glitchy, or data was just lost on happenstance? What if even if the arrest was unlawful the victim already lost their job?

If a body cam happened to be off, then it doesn't matter whether a law like this is in effect or not.

It does affect you if the police can force you turn off your camera, or if they can later claim in court that video evidence of their transgressions were illegally obtained, and thus inadmissible.

There is already a law that makes it illegal to get in the way.

Maybe it’s not working? I’ve seen examples of people getting in the way a lot. There’s nothing wrong with making more specific laws targeting bad behavior.

If that’s the case, how do more laws fix an enforcement issue?

Raise awareness, make it easier to prosecute - vague laws are harder to convict on.