In my personal opinion the reason for not releasing the original cuts lies in the differences he had during the creative process of the old films. Somehow he feels there's not enough of his "personal handwriting" in the films. That seems to be the case especially with the first film of the classic trilogy, whose production seemed to have cost him the most nerves. If there'd be a low-cost way to have the "sadly misled fans" get their "old and 'incomplete' movie trilogy", yet preventing that any new and 'unspoiled' fan gets his hands on them, he'd probably do it.

In a way he's already doing that by not interfering with community efforts to restore the classic trilogy in it's original form. I would not be surprised if he'd call them "fan edits" at some point in time.