I don't think that the point at which the mail is diverted is the issue here.

The article leads me to believe that the USPS took issue with mass-unsubscribing from junk-mail, not with having mail diverted before reaching the addressee.

The article was written from the POV of the guy who blew through alot of investor money on an idea that wasn't really thought through.

The USPS has a legal obligation to provide universal service to every physical address. They unsuccessfully tried to hack around it, while ignoring the multitude of solutions available to do so in a real (but perhaps inconvenient to them) way.