That implies there are other buyers who are happy to pay money to take it, doesn't it? That doesn't seem to be happening though:
https://qz.com/117151/us-states-banned-from-exporting-their-...
I suppose some countries agree to take the trash in return for some kind of economic favor from the US?
In many senses having an unpolluted local environment is a luxury good that many poorer communities "don't purchase" - i.e. a richer community would choose cleaner air while a poorer community would choose less restrictions on factories because they need these jobs; a richer community would implement proper wastewater treatment because they can afford to divert their resources to that infrastructure, while a poorer community would do without because they choose to spend their resources on more important things they're lacking.