Not really sure why this needs to be explained. There is no precedent to expect that they ever would. While they _have_ reverted and partially reverted mini gameplay-only reworks, that has never once extended to a full VGU.
So... stop asking. It isn't going to happen. They didn't sink tons of money into design, animation, testing, coding, voice acting, promotional material, etc. just to undo all of it. Nor to add on the _additional_ work of redoing all the animations and effects that they already worked on.
So there's just no reason to even think that they ever would.
Edit: Before anyone mentions it, Riot has never pulled an Ao Quang. And Smite's decision is more akin to just making a new character. It just happened that the stories fit better with the models swapped.
Second edit: Riot has also said, on many occasions, that they don't have those assets any more. So to "revert" a champion would require remaking them from the ground up.