But it's not a monopoly. FedEx can do ground delivery. Many USPS post offices have boxes for FedEx, UPS, etc. Oh, and btw, USPS receives no government funding.
And the main reason the USPS might have to reduce quality and availability of service is because of the discriminatory restrictions that the radical congress has imposed upon the USPS far beyond what other government entities (or private agencies) are required to do.