Blizzard/WoW got so big that it snuffed out all competitors and drove everyone else into the mobile game market. What killed MMO's without a specific platform purpose like GW2, (which we were lucky to get in the West, a few years later and we wouldn't have gotten it, I don't think) was monetization: Companies found a better way to make money (FTP with grind, pay-to-hurry, microtransactions/cosmetics, etc.) and that therefore killed the need to build worlds that encouraged exploration, adventure, etc. Basically, the old paradigm of the sub to D&D pen-and-paper campaign gave way to the micro-transaction for millennial smartphone quickie game. So MMOs died because it was so much easier to make mobile games that rang the Pavlovian bell so much more than camping for SoW Boots in LGuk. Meanwhile WoW sits there like Ogre on the barrel in Revenge of the Nerds and won't let anyone pass or grow; every other RPG that has come out has been more in the Destiny-mold. They are MMOs but nothing like what came before, because if they were, WoW would come find them and strangle them in their cribs. All the Asian MMOs suck for the Most part and while I enjoyed ESO and love GW2 (I am flirting with taking another character to 80, even though I have only one or two characters close to max or caught up with the Living World; I really don't like the expansions very much and find them tiresome) anything now that comes out will have to break new ground or risk being flattened or have a different set of expectations.
EDIT: To answer the thread, I know this puts me in the minority but I dislike dungeon crawls; I much prefer the open world. I like the cities and outdoor areas, the overworld and the wilderness. I love the way the world comes together when they do it right, the geography and the overarching world narrative. Its harder to do but done right everything works out so well.