This is only my guess:
1.A lot of people got tired of the endless dungeons/raids/tomes. they are looking for something else to do
2.Previous open world contents are lackluster (Dynasty Warriors style mobs,Fates,Leves)
The real solution:
1.Add more interesting open world content.
2.Fix the old open world contents (at least,bring back FFXIV 1.23 contents & difficulty please)
3.Hunts may need some tweaks too