Because that's not his job. You don't step on the nuts of you're manager. Makes him look weak to the boys in the clubhouse. If he didn't feel Manuel was getting the job done, then he should've battled to get him fired. You don't try and run the team yourself.
I don't think anyone here is on the Manuel for manager of the year wagon. He's not a great manager but when the GM is running the team from behind the scenes he's not the manager is he? Now Manuel will have to float by himself. With Williams out of the picture, if he doesn't get this team turned around, he'll be out of here.