I can only attribute it to people wanting to see how the trilogy concluded. I'm old enough to have seen the OT during first release (and re-release before the Special Editions). I was a kid, and memory isn't perfect, but I can tell you that every theatre I was in treated each film like an experience. Not religious, but some kind of group experience where we were all watching something amazing unfold on the screen, and it was thrice-in-a-lifetime. You know that crap TLJ defenders like to say about Empire being hated? Personal experience from the five times I saw it...everyone was caught up in what unfolded on screen. So, personal opinion, ROTJ made so much because people were actually interested in seeing how the story concluded. Same feeling for Marvel fans wanting to see Endgame.