There have been dirty diapers on the streets of El Paso, Texas for 30 years. I took the train once from Mexico City to Queretaro. As we were leaving the metropolis, headed toward Tula, the train passed through what looked to be a 15-mile long garbage dump. It was like the scene from one of those horror movies set in the future, garbage as far as you could see in any direction. I asked the porter if it was a huge dump and he said no, it was just property the railroad owned.
I recall noticing huge amounts of trash dumped on railroad property the last time I rode the train into New York City. This was 15-20 years ago. It wasn't as bad as your description of Mexico though.
Same situation in Sacramento. If you ride Amtrak east, you go through miles of trash left by “the homeless”. Actually the RR will clean it up and in months, thanks to the liberal policies of CA, it’s as bad as ever. Then they spend millions on a bike trail and allow the “homeless” (aka America’s Most Wanted) to camp out on it.