It's streamlining the interface, only showing the info that's currently relevant.
During week days I often pay attention to signs while I am walking/driving through to keep in mind if I will be able to park there on Saturday or Sunday. With these new signs - that would be impossible.
You also wouldn't know if you can park after the sign changes in general. If it says you can park from 3 to 11PM, what do you do if you arrive at 10:30 and you want to know what happens at 11? With a sign that shows all the requirements, it might say that parking costs money from 3-11 and after that it's free, or it might say that you can't park at all after 11. With these signs, you don't know until 11.
Better to streamline the parking restrictions themselves; that would make the signs simpler without hiding anything.