I awarded myself a Ph.D. in experience several years ago. Not recognized by any university, but it is real to me.
Answer: because correctly addressed mail can be rejected.
Case in point: Screen shot of address for Village of Airmont (https://airmont.org/) under ‘Contact Information’.
USPS: “Return to Sender; No such number; Unable to forward”
Old CW: USA should invade Canada
New CW: Canada will invade USA and China will help.
I am changing my voter registration to “Democrat” so that I can dine out at restaurants and travel wherever I like.