I always thought it was just his drive for success and being the center of attention, and to feel fulfilled. Or something. I mean, after being denied becoming a SeeD, I'd think he'd be feeling pretty bad and would want to achieve something so he doesn't just become an asshole failure.

Or maybe he was just controlled.

But anyway, my standard response, what does the UOG say for this? That would probably clear alot of things up.