As I understand things, Abrams turned Star Wars down (or more accurately declined to puruse it, do we even know if he was offered or in serious consideration?) becuase he's too much of a fan that he didn't think directing a Star Wars movie would work out.
And I hate to say this (I really do. Really
do) but he's right. Having a fan in power either as a writer or director is rarely a good idea, and can be worse depending on how much a fan they are. Take Superman Returns for example, directed by Superman uberfan Bryan Singer. That's not exactly the most popular Superman movie out there. Hell, it's taken seven years for the next Superman movie and that's a bloody reboot of the franchise.