You can beg all you want, meanwhile out here in reality that’s a list of duties. And the USPS is no where near irrelevant, they deliver more stuff in a week than any of their competitors do all year. It’s not their fault nobody sends you mail you like. If they hadn’t been saddled with a massive pension they wouldn’t even be losing money.
They don’t do letters of marque anymore because the military has grown enough to handle that. The duties that are why they were granted that power (provide for the common defense) still applies, they’re just doing it through a different method in the list. Got some other entry on the list that sends mail? No, thus the PO shall remain.
If there is a federal agency approximating the present USPS 20 years from now I shall be quite surprised.