Interesting how it’s remained successful for 8 years.
The appeal to the game is its story. People take breaks from FFXIV and return only to continue the story. This has been its model since A Realm Reborn first released. This is how Square-Enix develops the game.
All of its content–the dungeons, the raids, the Armory system, the Housing, the Glamor, the Gold Saucer, and Relics farming–are secondary to the story of Final Fantasy XIV. They’re all there to keep people entertained at the max level.
WoW only really has raiding, Mythics, and PvP and very little persistent secondary features to keep players hooked besides…grinding professions and hunting achievements, which FFXIV also does as well.