Now I know it's possible to actually drop one and not know it, but judging from the amount of them I see at other trails, it's not an accident. Somebody is just plain lazy. If you brought it, you sure as hell can take it home with you. Second problem, horses. I'm not sure what kind of agreement was made in getting the trials open for bikers, but it should not have included sharing the trails with horses.
Horses are the equivalent of motorcycles to trials.
They tear it up, badly. I used to live in an area where the bike trials were close to a boarding stable. Shortly after the trails were opened on land leased just to build trials, the horse riders found the trails. They ruined them riding them when it was wet. Anybody here who ever rode the Morrisville trials years ago knows what a motorcycle can do to mountain bike trails.