You are all forgetting the obvious. 20th Century Fox would have been releasing these not Disney. I suspect that is the real reason for this. Fox will hold the distribution rights for I, II, III, V, VI theatrical, DVD and Blu-ray for a number of years until they revert to Lucasfilm. But the original film rights release rights are completely owned by Fox. This delay is due to legal issues. Even a Blu-ray release probably won't happen until all that is sorted out.