I think a lot of the problem with imports to the US is related to the new regulations Trump & co put into effect on August 23, packages that have a value of less than $800 and are not business to business shipments.
As far as I understand it, the US removed an import code set that had been used without replacing it with a new one. The requirement for advance collection of import fees can be very problematic when returning packages, as to who covers what, etc.
I haven't studied the details, but I know that the Norwegian post office doesn't ship to the US right now, that's about 130k packages annually.
I think there are about 25 other countries too.