Give me dungeons that aren't a purely linear ordeal and I'll bother doing them again. The old cliche SE gave us when they started streamlining dungeons back in ARR was "Nobody did the optional stuff", to which I rebut; Of course they didn't, you put literally nothing worth doing behind those optional sections. Naturally players aren't going to bother with a side passage to obtain some worthless gear that's never even relevant, or worse something incredibly lame like an X-potion... A NQ X-potion...
Bring back dungeons with optional side paths, puzzles, heck maybe even throw in some optional mini-bosses? Then simply slap worthwhile rewards behind them. Tie them into things like Relic quests, rather than just "Clear this dungeon" as an objective, you can make "Clear this optional boss/puzzle/whatever in this dungeon" as an objective. Slap some new Treasure Map style content into dungeons, so a person can get the party some additional rewards for a quick detour. Get creative with it, rather than just copy/pasting literally the same layout of trash to boss every. single. dungeon. Just something to break up the monotony of these linear snorefests. Average Duty Finder group not going to do that stuff? Honestly I don't care. That's not an argument against adding something, IMHO. The average Duty Finder Black Mage exclusively uses Ice spells, should we remove Fire spells based on that?
Heck, with something like puzzles you don't even need a party... Just extend the amount of time we can remain in a dungeon after clearing. Everyone who hates fun can then leave, and the rest of us can stay and go clear the puzzles for additional rewards. Something like how the Nier Raid handled its content perhaps? Just with a bit more meat to it. So you run through the dungeon, clear it, then you get to explore it afterwards, with additional challenges/rewards/lore/whatever behind that.