I would argue that the people actually quitting and not just taking breaks and coming back when more content drops (which is completely normal behavior in every MMORPG) are not quitting because they ran out of grind.
They’re quitting because they’re no longer having fun. Generally a complete lack of fun is a deeper issue than “oh this patch is over for me”. It can be issues they have with the modern design of the game. Or it can just be that they’ve played for a decade or two and can no longer wring any joy out of doing essentially the same thing they’ve been doing since Cata (or Legion depending on perspective).
It is a good thing to simply be able to actually meet your goals in an MMO.
Forcing an endless grind just burns people out.
That said, I would say that:
- Leveling is too fast. I went from 53 to 56 from the completion bonus of 1 dungeon yesterday. That’s insane. Blizzard has pushed “only the current expansion matters” to an extreme so deep that they might as well remove leveling as a mandatory part of the game at this point, start everyone at max, and let them Chromie Time (at max) into older content if they want to see it. I don’t want this, but that’s the point we’re getting to. Adding 10 levels every expansion with only minor reductions in xp needed for previous levels wasn’t sustainable with how long this game has existed, but what we have now ain’t it.
- Gearing is too fast. Has been for a long time. M+ having no lockout was always a mistake, and Blizzard has really designed things for awhile now such that anything below Mythic Raid / Myth Track is inconsequential and something you can get over the span of 1 week if you have the time for it. Making ONLY the tippy top end matter is the exact same kind of unhealthy Raid or Die was. At least we have options for content to some extent now but it’s still not a good things how gearing is treated now. I still think being able to “finish” until a new patch is reasonable. But there’s a middle ground between where we are now and “you never finish the patch”.