I also get the impression that a lot of folks at Lucasfilm would love to see the original versions released, but they don’t want to thumb their noses at Lucas’s clearly and repeatedly stated desire to have the revised versions be the only ones widely available.
I know a couple people at Lucasfilm have said as much publicly, as well. It’s not a contractual thing, or a stipulation, or any of that. They just don’t wanna piss him off if they don’t have to, and they don’t have to. So they won’t.
Doesn’t mean they won’t ask every now and again, like they did for the 70mm re-release. And maybe they also asked, right around the same time, about putting the originals on as a bonus feature for the 2020 UHD/BD set. Who knows. They maybe didn’t. But they might have done.