And how does the postal worker delivering thousands of letters addressed to "UPS Headquarters ATLANTA" to a dude's apartment in Chicago not think it strange and report it?
Just an anecdotal data point, but, in the year and change I lived in Chicago (relatively recently) I experienced the local USPS quality of service to be... extraordinarily lacking.
They probably use their own services for important deliveries. Besides, if USPS don't report strange/dangerous USPS delivery activities, who else would?
I guess everybody who tried sending mail (including checks, apparently) to them and never got through would suspect something is wrong and report it...