This was already discussed before but I'm doing it again
Why would Richard Donner make his own cut of Superman II and put such a stupid ending on it? I know when he made Superman back in 1977-78 he was making both films at the same time, but the producers wanted him to finish the first one and finish the second one later so they could get it released, so to cut corners he put time reversal scene that was planned for Superman II at the end of Superman The Movie, which didn't really work. Then he was replaced by Richard Lester to figure out how to do Superman II.
The Richard Donner Cut of Superman II is much better, and the time reversal makes more sense in this movie, but the stupid diner scene at the end although funny did not belong there.
If Superman reversed time none of what happened in Superman II ever happened, so the diner scene where he got his butt kicked didn't happen, so him going back to the diner for revenge didn't mean squat. No would even have knew who he was, just nerdy Clark Kent with his big glasses (a very clever disguise for any super heroes, Lol).
Don't even know why I brought this up, bored I guess!
Final thought watch the Richard Donner cut from 2006 instead of the original Superman II from 1980. Except for the nonsensical ending its much better!