It's sad because Vinny and Ari had a deal in the beginning when they met that Ari would make Vinny a superstar no matter what. Also they have a close relationship with how it is right now, it's obviously going to change if Ari takes this job. Vinny might be able to get any job at Warner Bros. but that's not even a guarantee. Ari as an agent would get Vinny a job and no matter how good or bad the movie did, they would still get paid. As a studio head though, he has a lot more responsibility and if a couple movies bomb, he's out, so he has to be a lot more careful with what Vinny can do.