For some it is simply a part of their culture to not think what they are doing. I still remember when I was 10 (about a millennia ago) seeing a neighbor pour motor oil down a storm drain. This was i Dallas in the late 50's. People did this and didn't think anything about it. Now I see signs painted around the drains against putting anything in the drains. Obviously we have to be taught.
Thanks for this, you just helped me solve a riddle. Last summer a 3 way stop was put up at one entrance of the supermarket. No one could figure this out as there is very little traffic at this point. A culvert was put, at the signs, across an existing shallow drainage ditch as a crossover point. Months later a crew came out and deepened the ditch and then put a fence along the part dug out. I just read about the county's swale program [tenthacrefarm.com]. When I walk to the market I often see trash in this ditch. I suspect the fence is to keep people from falling into the swale and to keep trash, which can clog the culverts, out. I have found there are always reasons for things we think are silly.

My late partner and I traveled to Viet Nam. There was mountains of trash everywhere and it was scary to see run-off going into the bays and rice paddy's. After we got back, I started carrying a bag with me and pick up every bit of trash I see on our route. Twice a year the county has a leave-no-trace event and many of us get together and select a route to walk and pick up trash

Check out the video. This was 5 years ago and it continues to grow.