I agree, we're trying our best with PD trainings and coming down harder on unprofessionalism in PD, but we still get little to no RP out of anything. I think that this could be affected quite a bit by the revive rule where you can't be arrested after being revived. This increased the amounts of shootouts and decreased RP a lot overall. We're also working on official quizzes and official trainings to be hosted at least once a week for all PD.
As for other departments, they all have quite a lot of people but you may not see them very often.
It would only take a couple rules to change to make a big difference and to increase roleplay as a whole.