CBS has control over whether new series will be made, which frustrated JJ Abrams and is a likely contributing factor to his leaving Star Trek for Disney's upcoming "Star Wars VII" project. (15 May 2013)
Abrams doesn't own Trek. He was always playing with someone else's toys. Paramount gave him more or less a blank check with the movies
, but that's as far as it goes.
As far as why Abrams left directing Trek for Star Wars, I think that's just a case of him having always been a really big Star Wars fan (even before he came to Trek), and it was too tempting a gig to pass up.