Maybe the people who have dementia are the people who the aliens took the consciousness out of the body and the trash left behind is the body vessel that the aliens know will eventually die and decompose into the ground. Maybe that's why someone invented caskets so that way the nutrients from the human body that was eaten from the bug who was eaten by the next animal and went up the food chain until it was the human that ate the cow that ate the grass, doesn't get the nutrients back tonthe planet because the nutrients for the planet are trapped in the caskets. Thats gotta be the cause of the environmental crisis cause the earth is in survival mode and the aliens need the Dementia patients to wonder off, "get lost" and die so at least the planet can get back some if not all its nutrients it let the beings barrow before someone discovers the body.