highway and waste

Today I walked along a path that runs along under the highway. I was once again very shocked. I was shocked at the amount of trash. And surprised. Amazed what things people throw from speeding cars. Shoes, jackets, paper, bags, cups, bottles, packaging, newspapers, trash bags, wooden slats and more.
Why? Why do people so? I do not get it. On motorways there are huge dumpsters at each parking lot.