I maybe wrong but just taking a guess. I could see CBS having an issue with their prime announcers being used with other network logos.
Now if they were to keep what they have now and use that as CBS and then use Fox's #1 team which I believe Aikman and Buck with the FOX logo it may work out. I would be very pleased with two commentary teams, it would really freshen things up on a week to week basis in CFM.