I think his motivations for turning back in at the end of the Donner Cut were more than erasing Lois's memory. Its about undoing everything. Zod never took over the world. I think the original intention with how it was written was it was a what-if or imaginary story. Everything that happens in the film is extreme for a typical Superman story of the time. Lois learning the secret, giving up his powers. But even more villains taking over the world. You never saw that in the comics, he would fight and defeat the Phantom Zone villains before they got that far.
I am not saying this was a good idea. Its an odd approach for a second film. Its sounds more like an episode of a long running tv series. Maybe they were counting on how well known the Lois/Superman/Clark relationship was. So they decided to show what if all the preconceived rules are broken but lets undo it at the end. They never had the intention of changing the status quo permanently. You never would have seen that back than.