> if I can sell a digital item and lose access in the process
Which is exactly the problem with digital media – how do you prove that to the satisfaction of everybody involved, i.e. especially the rightsholders?
On the one hand, the fact that almost all of the music market and parts of the e-book market for example operate without DRM shows that in those cases the publishers/labels have somewhat resigned themselves to trusting the users to remain relatively honest in that regard, but I suspect that a platform explicitly designed for reselling digital content would still draw some additional scrutiny of the unwanted kind.
Somewhat ironically, DRM would solve that particular problem – at the price of introducing additional restrictions during day-to-day usage that I wouldn't be happy about, though, either.
E.g. looking at my personal music library, it would likely restrict the choice of software players and good luck implementing that kind of personalised DRM with hardware media players which might not even have any kind of internet connection. I've also invasively (albeit losslessly reversible) applied replay gain adjustment to my whole media library because some media players and e.g. my car radio don't support the tagging-based adjustment, and in some rare cases I even had to edit some files [1], neither of which would be possible with DRM-protected files.
And of course it would introduce a continuing dependence on the existence of whoever is providing the DRM in order to access those media files you've supposedly "bought".
[1] The version of 3:47 EST on iTunes turned out to be missing the mouse squeak at the end – because of no DRM, I was able to find a complete, but otherwise slightly worse-sounding version (more surface hiss) on Youtube, lift the squeak off of it, de-noise it, and tack it onto my purchased version without having to lossily transcode that the main bulk of that song again.