Side quests etc not enough

Why do we have side quests for the storyline?
That very question has popped in my mind several times.
I have done every side quest there was in the areas that storyline has send me yet I run into several times where the side quests are just not enough xp to keep up with the storyline and then like for instance now I am lacking half a level worth of xp.

Fates as much faster than side quests, requires less effort.

I thought the reason we had side quests was so that they could fill in the xp the main quests did not give and so we could feel that a storyline was more than just the main story.

Yet I find the side quest xp to small, the gil laughable and the rewards just way to late, by the time there gomes any gear worthwhile in sidequests I already have had the same or better for 2 levels.

So please tell me, why do we have the side quests, they seem to be just a distraction from grinding fate and main storyline.

I think they are there to give more "lore" to the game. I agree that it is a weird designer choice to not have more quests. I start to think it is because they want to force you to enter dungeons and to learn your class but that seems to not be working because FATEs give infinitely more xp :S

IMO they do this to make you grind a little bit either in the world or in Dungeons. Besides the Hunting Logs if they gave you all the experience you needed with side quests then why would they even need to put mobs on the map? You can also fill in the missing with Levequests.