This was happening in my part of town... the business owners were complaining about the trash and human fecal matter. The city finally put up signs that limited parking for two hours and they all left.
I parked in a place where it was normally OK to park past 10pm. When I got to my car at 10:30, I saw a ticket on the window. Then looked at the parking sign, and found out that it was new and that there was no parking allowed after 10pm.
No doubt the times were changed to keep people moving along.
As Kyle or Stan would say: Bastards!