If you ever wonder why you get so much postal spam, this is why. The USPS is mostly funded by advertising. They could, for instance, stop the practice of accepting "deliver this junk to every mailbox in this region"...but then they'd go bankrupt.
I'm not suggesting the USPS should be filtering by content, just taking the programs that exist specifically to facilitate postal spam and consigning them to the dustbin of history. Those programs essentially exist because they're a primary funding source for USPS.
1. Mandate universal delivery of letters regardless of distance or remoteness, even out in some wilderness region of Alaska, guarantee everyone the right to get a letter for the same stamp price as to deliver a letter from one office in the Chrysler Building to another one.
2. Have USPS not get taxpayer funds for anything
3. Impose arbitrary price controls on postage based on Congressional vibes
4. Have postal employees still be federal employees and qualify for cushy benefits and retirement (I assume this is there because their unions would strike if it was taken away)
5. Micromanage how that retirement plan is funded
6. Give USPS special privileges like the one being discussed... or like the basic monopoly on 'delivering non-urgent letters' that bars UPS from delivering mail into your mailbox.
If all the above sound extremely confused, that's because the USPS has been the object of political meddling for at least 5-6 decades, so it still shows the fingerprints of many ideologically-conflicting schemes and agendas all at once.
If postal employees are federal GS employees, they are not legally allowed to strike: