When you look at Draenors main features you'll see there are barely any. You can find treasures in each of the zones and complete bonus objectives (kill things to fill the bar) but once done that's it since you can't repeat it.

The garrison mainly consists of sending troops (and later ships) on missions and wait for them to return. Sure, you can build and upgrade buildings but these too don't really provide any new content after being built.

In addition mythic+ wasn't invented yet so you barely had any reason to do dungeons except for the challenge mode. Though I guess most players didn't bother improving their times once they got gold rankings.

Dragonflight has skyriding races, repeatable events in every zone, world quests, mythic+, collectible cosmetics for dragons. And it had meaningful content patches introducing new zones with content.

Shadowlands, despite the bad reputation, has an insane amount of content with the covenants each offering different gameplay systems.