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I hadn’t thought of it like that. There was quite a bit of “last chance to buy X” adverts and promos back in the 80’s and 90’s as various formats progressed. Like you stated, Lucas was at the forefront of technology back then, but I can’t remember thinking at the time of “One Last Time” advert was because of the onset of DVD, or other format. Although that is probably because of the delays in the format specs in the Wikipedia article, and DVD not really hitting the stores until early 1997.
I do agree with the OP: “Personally, I would have preferred if George Lucas did this instead of messing with Irvin Kershner and Richard Marquand’s films”, and that George just tinkered with his own film, offering the original cuts alongside the changed version.