The issue at hand here seems to be Redbox selling the access codes separately from the DVDs, whereas Disney wants them to be bundled together.
I don't think people buying a new textbook and reselling the bundled access code is a big concern for the publishers - the online content is supplemental to, not duplicative of, the textbook content.
Access codes are really what publishers are banking on for lock-in, and they will happily sell students one sans textbook. It ensures the publisher gets a piece of the pie, regardless of the used and rental markets, or piracy.
Edit: after reading online, I think you are probably right but it seems like a dumb deterrent and inconsistently applied.
[1] https://www.fda.gov/Food/GuidanceRegulation/GuidanceDocument...
They can ask if they want, but they have no legal leg to stand on.