You want to know why? Check out Behind the Bastards two parter on Reinhard Heydrich, noting his time running the Sicherheitsdienst (SD) in Berlin. TL;DL Heydrich eventually just made a list of people the party didn't like (based on what he didn't like) down to transients, people with mental illness, and people with jobs he didn't approve of.
This is not our first rodeo.
Here's the thing (other than basic enshittification):
For a lot of rural and wild (mountain and desert) places in the US, USPS covers the last mile (or last 100 miles) that no other service does. At a loss.
Private delivery service gives no fucks. We know this because UPS and FedEx or any other hand their parcels to the USPS pony headed out beyond the pale to keep their oath.
If we privatize, then those places vanish. They also stop paying taxes.