A comment on a
similar thread from user Lgibjones on The Paceline which makes intuitive sense to me::
The exemption existed because the administrative costs exceeded the funds that were recovered.
Also over there (user Tycom):
I've read some reports that the US administration are trying to have the foreign postal services collect the tariffs and duties and forward those fees, effectively offloading that workload.
Part of the reason then that foreign postal services have paused deliveries right now is not only the ever changing rules, but that they don't have systems in place to deal with the above as it's an all new obligation.
Again, it makes intuitive sense to me that all these foreign postal services would stop shipping low-value stuff to the US nearly all at once. None of them had the necessary infrastructure in place to handle this new thing.