Why can't people pick up their trash?

I was playing outside this morning with the dogs, and Zander runs down to the next apartment building and is rummaging on someone's back porch. I walk over to see him eating this beef stew in a garbage bag, so I pull him away and see all sorts of maggots in the food. I am TOTALLY grossed out, needless to say! Zander will be getting NO kisses from me anytime soon either. I just don't understand why some people leave garbage on their back porches for the birds and dogs to get into. We take our trash right from the garbage can to the trash can....that only makes sense to us. Thank goodness these tenants moved out, so hopefully I will not have to deal with this again....hopefully the next tenants will be good about removing the trash. So there is my vent for the day!