I really can't. The only argument I see is "we can't allow it because every customer is a potential thief". What will enabling resale cause? Piracy? Well piracy is happening regardless. People who want to illegally download games can do it today in one click. Instead the piracy excuse is being used to restrict legal resale so you have no option but to pay the publisher's inflated sale price.
By allowing resale of digital copies outside of platforms all you get is essentially the complete repeal of intellectual property rights for digital media.
I think as a compromise I'd be okay with some kind of license database (maybe blockchain-based, maybe not) that keeps track of who owns a legal copy of what. People reselling digital copies of copyrighted material would have to transfer ownership of that license to prove they're conducting legit business and not just minting new copies out of thin air.