You got to level 80 and that was it. You were done with the majority of zones except for pockets of endgame daily quests in Storm Peaks, Icecrown and Sholazar.
You finished farming gear from dungeons and that was it. You were done with dungeons for the rest of the expansion except for the daily badge quest which really wasn't mandatory if you were raiding.
You finished farming gear from raids and that was it. You were BiS in every slot and then could push rankings or just chill out and play alts.
You finished farming reputation and that was it. You bought all rewards from the vendor and never went back to grinding rep for that particular faction.
You leveled professions to 450 and that was it. You didn't need to collect new recipes and grind new herbs every patch.
In BfA...
You level to 120 and that's not it. You still have to run WQs in every zone every day to farm AP lest you fall off the treadmill.
You finish farming gear from dungeons but that's not it. There's an infinitely scaling system where dungeons get progressively more difficult meaning you can never beat a particular dungeon.
You finish farming gear from raids but that's not it. You'll never be BiS because you'll never have items that titanforge to max in every slot, have a tertiary and a socket on them. You'll keep grinding forever.
You farm reputation to exalted but that's not it. You can't just buy the rewards. You have to keep grinding that rep in hopes of getting a lucky drop from the supply chests.
You level professions to 150 but that's not it. A new patch comes along with more levels to grind and new recipes and herbs to farm.
Good thing people enjoy repeating the same content ad nauseam, am I right?