This your first mmorpg? You grind for everything. I play WoW and after raids you work on getting every mount, every title. Same stuff you do here.

Have you completed all the ultimates, solo potd, hoh, mastered every craft. If you want an real endless grind go play bdo or something til next patch. If you've finished literally everything in the game and have 100 percent finished achievement book and literally nothing else to do well then you do what you do anytime you beat a game. Play something else bdo might be up your alley it's unbeatable. That or shadowlands comes out soon.