The problem is that very few, if any, of the people camping at Deep Creek are thru-hikers. The PCT permits are designated for through hikers only, not people intent on camping solely for the purpose of going to the springs. The bigger problem is this- most of the trash comes from people camping overnight down there. Plus there is the sanitation issue.
The USFS is understaffed. Otherwise they would be going there regularly and ticketing these people.