These cities expect to gain traffic law compliance in the form of fines issued for breaking them. On the other hand, they know what the law is and just ignore it because, "what are YOU going to do about it."
How would they like it if one of their officers stopped a guy going 45 in a 30, and just said, "Yeah, I know I was speeding, but SCREW YOU, you can't do anything to me."
Glenn