The DA is not their boss. Cops are supposed to enforce laws. The DA is supposed to prosecute them. The cops are just using the DA as an excuse to not do their jobs. And once you normalize the cops not arresting people, now the DA has an excuse for prosecuting fewer criminals - at that point how do you decide who's to blame? Now you have two dysfunctional organizations, each pointing the finger at the other, and you've already normalized at least one of them. Even if you think the cops shouldn't be arresting people because of the DA, at the very least this skews data on crime as police are making fewer arrests independent of crime levels.

This is like me saying I don't want to do my job because those other guys in the other department aren't going to do anything with it, so I'm just not going to bother. I think almost everyone can relate to lazy/incompetent coworkers - does that give you an excuse to stop doing your job?