Reasons why i play any MMO:

1. Sense of progress (basic addiction for any MMO)
2. Sense of achievement (same)
3. Social aspect - having great time with friends, instead of for example going out to drink with them IRL i would rather spend time in game doing something challenging and sharing that experience with my friends.

Why do I play this game?

Same reasons + the fact that i'm a FF series fanboy that loves to see how the game evolves, how it grows and becomes better with every patch and believes that soon it will become so awesome that there wont be ppl like you left who don't understand why they should play this game