Because at a big agency, if there really is a problem, they can just move you to another area. In a small city, once you are targeted, you have nowhere to go. It's a choice an individual has to make, but don't think that a small city is somehow more friendly to the cops, they aren't. Often they can't decide what they want you to enforce, for example, the mayor may say they want you to enforce parking ordinances, but when you ticket the "wrong" person, shazzam, you are up in front of the City Council