I think part of reason people feel this way about cops in particular sometimes is that a lot of their job is to go around monitoring things. It is hard to detect if they are actually working hard or not. Crimes are rare and noisy. If a doctor spends all day playing on their phone, the patients will notice. If a cop does—it was just a low crime day, maybe.

Also the general public has more opinions about the behavior of governments employees.

I dunno how to actually feel about this, from a “is it good” point of view. But I can see why people feel this way at least.