The vast majority of first-class and bulk-rate mail is not anything can't wait a few days. For truly urgent deliveries, use a courier service or pay a higher postage that covers the expenses of that.
And that's why it (unfortunately) won't happen lol the USPS is as much of a jobs program as it is an actual mail delivery service.
As the guy above you pointed out, the postal workers union exists, and would fight this tooth and nail. Additionally, without legislation forcing it, management at USPS doesn't really have any incentive or ability to fire 1/2 to 4/5ths of their workers, those saved tax dollars don't really matter to them.
As much as I agree it could be made much more efficient, doing so would probably be very unpopular politically. For as often as people have negative experiences with the USPS, no one wants to see their friendly neighborhood post carrier (who walks around in a fun outfit dropping off letters and packages to them) get canned.
With all due respect, fuck off with that shit. The Postal Service is a Constitutionally mandated utility network substrate, and it's ability to get packages from one end of the States to the other reliably is already suffering. As someone who has been shipping things recently, I'm damn well tired of having to resend things due to spoilage/mis routing/etc...
There is a certain regularity with which operations should execute in order to be functional, and we're really behind in interstate shipping.
And to be frank, everywhere should be similarly burdened with pre-funding pensions/health benefits.