I think what parent is saying is that in the US a disproportionate percentage of USPS budget is spent delivering mail to extremely rural areas (far from both cities and small towns).
Only later that I discovered I was the dumb one.
IDK how you can possibly economically send mail to places like foreign barely habited deep pacific islands for the same price as mailing to your neighbor.
China does that, for example - which is why you can get a $3 widget on AliExpress sent from China with free shipping.
However, right now congress doesn't act like they're doing that intentionally. That doesn't seem to be the policy they're aiming for.