Someone a few years back offered to restore the originals for nothing. Lucas never responded. It obviously goes much deeper than ‘it costs too much money’.
Well, that may have just been an easy cover statement rather than explaining that he just didn’t want to. But remember, nothing is free, while he may not have had to pay Robert A. Harris a salary, he would still have had to have funded the restoration and paid all of the other people who were working on the restoration. It also would consume his time as he would have no doubt supervised it, while simultaneously trying to supervise the other project that his changes were being added to. Maybe that’s the case, or maybe he did want it to never be seen again, who know? Now that he is gone however, that is irrelevant to whether it will be released now, which I think will either be when TFA comes out on blu-ray, or when the 40th anniversary happens alongside Episode VIII.