Not trying to be too argumentative, but I would assume WJBK has an agreement with the Fox Network to carry their network programs. I'm sure the network would balk at giving up prime space 5-6 nights a week to local programing. Especially in a market the size of Detroit.
The sub-channel, which is most likely on most cable systems, whomever it may be Comcast or whatever. Placing the games on a channel that carries old movies, western, detective shows, etc gives Fox the opportunity for extra revenue. Since WJBK is a Fox owned and operated station I really don't think the parent company would allow the move.
As I've said before, if the Tigers go to over the air TV it would be to someone like Channel 20. Either that or they'll set up their own streaming platform with the RedWings with the help of MLB Production facilities.