Zachski: Probably because by the time of the fifth game, your work in Spielburg was relatively uneventful compared to your events from the second game onwards.
Elsa remembers you, of course, as does one other character, but compared to the global scheme... the only thing you did was displace an ogress and save a princess. After that, you've consistently been saving entire countries (and then the entire world) from oblivion, so yeah.
Also it might be allowing for a canon unwelding - keeping it vague whether you drove Baba Yaga out or not (even though QFG4 established that you did even if you didn't, out of plot necessity) and thus whether you were
truly deserving of the title of Hero of Spielburg or not.
Let me put it this way by relating it to art.
When you're listing your accomplishments as an oil painter, do you include the macaroni art you made in 2nd grade as an accomplishment? :P
Just for the record, you are supposed to have helped a prince as well as a princess. I know it's possible to beat the game without helping the prince, but QFG5 assumes you helped the prince. Elsa left Spielburg because her arrogant, dumb brother is in charge at that point. I assume that means you helped him.
But maybe I'm wrong? Maybe QFG5 is meant to leave open the possibility that you didn't help Barnard, but he became king anyway? So Spielburg is now being run by a bear, and that's why Elsa left? I hadn't considered that before, but I love it!