I think a lot of it is newer campers. We camped as kids and no cutting through other's spots was drilled into us. Probably a good start on this would be this rule posted prominently among other rules. A friendly chat with offenders my be in order depending… I don't like it either but it is pretty harmless if it doesn't happen continuously. If it does some action is in order.
Litter was the thing being cleaned up when I was a kid. It was far worse than today. Many respectable citizens of my grandparents generation thought nothing of throwing stuff out of the car (born about 1900). I can't see any overall trend towards selfishness, people are just people. The good the bad..