Trashing the shuttle train

I am amazed at how trashed the Franklin ave shuttle train gets, even though there is usually someone at Prospect Park with a broom that cleans it out every run. People seem to think it is a 2-car rolling trash can, not to mention spittoon (on the floor, really?). I've gotten used to people throwing their trash all over the streets (again, why?), but the dinky train so many of us use and have to share? I am trying to understand, but all I can come up with is selfish and lazy people.