For me it's just that strafing around an arena blowing up dozens upon dozens of enemy tanks is not enjoyable. I don't want to do it, and there's no way to skip it or mitigate it in any way. I loved Asylum and City because I found it so fun to be Batman; loved stealthing, loved fighting, loved gliding, loved solving puzzles. Arkham Knight still has all that, but mixed in with those things I do like are what feels like endless tank battles that I actively do not like. I don't want to do them any more. I just don't want to shoot another tank, end of story. So when I think about maybe replaying Arkham Knight one of these days, I'm just completely put off by the thought of having to blow up like 500 tanks per playthrough.
Honestly, take the cannon off the Batmobile and Arkham Knight becomes a much better game. I actually loved driving it around Gotham, and I mostly liked all the puzzle solving you get to do with it. I even liked the Riddler races. It's solely the sections where you get locked into a circular arena and have to shoot dozens of drone tanks that I hated, and there are so many. Just cut that shit out. Change the story so that the Arkham Knight doesn't have hundreds of drone tanks ready to drop into the city and bingo bango, it's a better game. Still not an amazing game, but a much more enjoyable one.