Doesn’t seem mystifying to me at all. It’s totally normal for companies to produce something, make alterations, move on to something else.

Look at all the different versions of Apple products over the years. Nobody at Apple keeps track of that sort of thing, because it doesn’t matter. Only nostalgia-driven fans and a few historians care about it.

I’d say Lucas is kind of unusual, because he kept most of the production material associated with his films - costumes, props, drawings, etc. Most companies dump it.