Yeah but there is really no way to enforce a single resale other than extensive DRM measures, which is the whole thing we want to avoid.
By allowing resale of digital copies outside of platforms all you get is essentially the complete repeal of intellectual property rights for digital media.
But, on the other hand, without IP, DRMs lose a lot of their power. Once the DRM is cracked, the protected data can be freely shared once more. The only usefulness for DRM in most industries would be preventing unauthorized copies in the first days.