Imagine you're a programmer, or a chef, or a carpenter, really anything. Now imagine you go to work every day, put in 8-10 hours a day working hard, and at the end of each day someone in a more powerful position than yourself throws out, ignores, or otherwise destroys all of your work for that day.
And this happens every day, day after day. No matter your work ethic or how much you care about your job, sooner or later after enough of your work is sabotaged, you're going to give up.
So no, I do not expect the police to "do their job" as you put it, when a chief prosecutor publicly and vocally undermines that work each and every day. If you can't understand that very fundamental human reaction, then I don't know what to tell you.