I can’t believe they deliver mail to a good share of the places they do without guns.
It’s to keep the post offices themselves secure, more likely. Honestly, we have had a spike in whackjobs participating in mass shootings of formerly safe sectors of our society. Best to secure those locations. If you put a bunch of cops or National Guardsmen there, people would scream, “BRAVE NEW WORLD! BIG BROTHER!”. Better to just have the arms on standby and avoid as much lunacy as possible.