There is no clean cut reason why XIV > WoW. But if I had to pick some.
XIV story flows, like reading a book... WoW story is choppy like reading a paragraph in one book, then another, then another.
In XIV gives a feeling of the little things you do add up to something great.
In WoW they tried to make every task so epic, that it feels pointless.
XIV has my 3 wife's Shiva, Garuda, Siren.