I currently am sub'd, but only for classic TBC. Since this is in the retail section I assume that means what would bring me back to retail.
A lot of it has been covered here already, but the bloat each expansion and constant need to play all the time and do things I don't want to to keep up. That is why I enjoy TBC, if I want to take 3-4 days off to do whatever, at any point of an expansion, I don't feel behind at all.
I was subbed for Shadowlands, leveling was fun, 5 mans were fun enough but then it just stopped being fun. The chore set is quickly. Do world quests, farm anima, do torg, do the maw, do PVP. Of that list, doing torg was the only "fun" thing on it. Torg quickly became unfun after doing the same boring crap with just a little more hp/damage and zone appearance.
What I want and what would bring me back. Level up > do 5 mans(a few days, 3-5 worth) > be able to raid high end. World quests can give gear close to 5 mans, that's fine, can be used to fill in missing items that didn't drop. That's it. Nothing else required for high end content.
Torg would be merely story/cosmetics. Maw would be merely story and daily quests for gold. PVP would be strictly for pvp gear. Mythic+ would be strictly for M+. The cross over of everything makes it almost necessary to do all aspects of the game even if you don't want to and/or find them very unenjoyable.
Finally, lore. I am a decently sized lore nerd and blizzard has just run it in to the literal ground. Everything has been retcon, no one dies, no decision is final, nothing maters. Good chars are turned bad, bad chars turned to shit with horrid story(Sylv). Any single person on the warcraftlore subreddit could do a better job writing a story that makes sense and has good twists and turns to keep people interested and they'd probably do it for free. The fact that people are getting paid to fuck things up this badly is near unfathomable.
So to bring me back to retail, break apart the game to Raiding, M+ and PvP where each side never has to touch the other if they choose. Limit all things but those previous 3 to purely optional and by that I mean optional, not "oh it only gets you some sockets" or "it's only a few ilvls" as that isn't optional to any decent raiding scene. And fix the fucking story/lore.
As I don't ever see any of those happening, WoW retail is dead for me. Thankfully classic is a thing to keep me around my friends.