Old WoW had clear-cut goals and a structured character progression path to follow. You would do dungeons and heroics until you got BiS and then you would put dungeon-grinding on the backburner and stick to doing only the daily heroic for badges etc. You would do dailies for an X amount of days until you got your desired reward (be it vanity pets from Argent Tournament or enchants from Sons of Hodir). You would finish a raid and then move onto alts or other aspects of the game.
Modern WoW trades this progression path for a set of rather nebulous goals. You keep running WQs (which are really just dailies), normals, heroics and mythics indefinitely because you can almost never get BiS from them (and legendaries are by far the worst offender, being extremely rare and boosting character power in very strong ways). This is exacerbated by the fact and you can now get raid-equivalent gear from aforementioned content. Rep gains have become grinds (WoD) and more recently randomized grinds (Legion). You keep running raids including lower difficulties even after clearing them for a chance at warforged / socket / tertiary. Basically, the game is built in a way that has you endlessly chasing a carrot on a stick. In my opinion, games being "beatable" is one of the staples of gaming that shouldn't be sacrificed in favor of "endless content".
tl;dr I don't really feel my character growing when I'm running the same dungeons on the 365th day of the expansions as on the 1st.