One of the reasons is that I haven't enjoyed any other MMO to be released recently. Aion, Vindictus, DCUO, Rift... none of them could hold my attention.

It's true that there's not much to do but level and do the few storyline quests that FFXIV has, but I still find it enjoyable. The key for me is that leveling is enjoyable. And like everyone else, I think it comes down to LS, friends, and doing things with a group.