The common argument is if USPS did not have that monopoly, then other providers would enter only the profitable regions.
The result would be the USPS would not have the revenue to serve the unprofitable regions, and would either be forced to end service in the unprofitable regions or simply collapse.
The result would be the USPS would not have the revenue to serve the unprofitable regions, and would either be forced to end service in the unprofitable regions or simply collapse.