1) Lorewise, its just more interesting, and in terms of genre, FFXIV has a rich science fantasy flavour, with its technology being in a sort of magic technology industrial revolution.
2) FFXIV is more consistent than WoW with storytelling. If some hidden information needs to be made known in FFXIV, its made to be a shocking reveal that leaves a lot of questions open to be answered. WoWs story was all over the place when I played, and reading up some of the lore later on didn't leave me impressed.
3) I don't have to raid in order to be a good player. I can always choose to raid, and I have done in the past (still need to start SCoB though), but I don't feel as though I'm FORCED to raid in order to get the main story.
4) No need for alts. I hate alt-itis.
5) This one may be my fault, but coming from FFXI where I went in with no friends and made them as I went along, WoW was far too lonely. With FFXIV, I've continued to meet new people and speak with them.

Thats why I adore FFXIV.