Is it true that police officers have a speeding ticket quota they must meet every month? If so, why?

Towards the end of the month, if I see a person pulled over for speeding by a cop, I often hear from whoever I’m with that the cop is trying to meet a quota. Is this true? If it is true, what possible reason could there be for such a quota?

I put this in the general section specifically to avoid comments like, “because cops suck,” or “because the government is stupid,” so please keep those comments to yourself.