It’s all about narrative.
Something you’re obviously overlooking.
The SE was to tie the OT more directly to the prequels (and in the case of '97 especially, test the technology for the prequels).
You can hate the prequels and think the SE is garbage, fine, but that’s not the point.
The point is that George said countless times that I - VI is meant to be one big long movie, with each “episode” being just a snippet of said story.
So in regards to the overall narrative, it makes perfect sense for the celebration scene to be in there because ROTJ is the end of this 12 hour long story; the climax that ties everything together.
You can say George is full of crap and that you hate it, but that’s not the point.
You can say it makes no sense if you just watch the OT by itself, but that’s not the point, because I - VI is one long story.
If you don’t like George’s view of “one big 12 hour movie”, watch the OOT and pretend nothing else exists, nobody is going to stop you.