Because waste systems are very effortful. It would simply take lots and lots of labor to gather, transport, and dispose of all that trash in an organized way. L

Because waste systems are very effortful. It would simply take lots and lots of labor to gather, transport, and dispose of all that trash in an organized way. Labor that is currently engaged in producing food, clothes, etc. Think about the relative population density in many of these cities as well. And the relative productivity. Not at all an easy problem to solve.