They’re trying to figure out when the best time is to release it. I don’t think there’s anything intentional going on to deprive ‘Tron’ fans of the new edition.
I call complete bullshit on this. Disney would only withhold copies of Tron (AKA completely avoid flooding the entire market with Tron DVDs) if they believed it to be financially advantageous. And with graphics and plotting that are incredibly dated, waiting until after Tron Legacy has made its millions before re-releasing Tron is probably the best move.