Okay so I originally assumed this was probably due to some union rule or something like that. But I didn't find any reference to it in the NALC guidelines, anything in the USPS resources center (which is hard to use), anything in google searches, and the original employee documentation or spec.

I did find the USPS History section and it turns out they have someone whose job title is "Postal Historian", Stephen Kochersperger.

But, anyways, I found the address (not email of course haha) for the USPS history office so I have wrote up an letter and put it in the mailbox. I will eventually update yall

This is the case for most "Dumb laws": there's an outlier that becomes kinda silly, but it's not really worth the effort to change.

I saw one "It's illegal to hunt Blue Whales in Idaho". Because it's illegal to hunt endangered species in Idaho, and Blue Whales are endangered, not because legislators were super concerned about saving Idaho's whale population.