Whatever the explanation is, if you were still holding out hope for the unaltered Original Trilogy to drop on Blu-ray or streaming someday, you’ll either need to keep waiting or just make peace with the fact that it likely won’t happen.
J.J. Abrams didn’t elaborate on these reasons that were given to him, so it’s unclear if Disney’s just unwilling to release the original cuts, if the company is legally prohibited from doing so due to an arrangement with George Lucas, or if it’s perhaps just impossible due to the physical sources being changed.