It just is hard to make work.
Most important thing is splitting 1st team practice reps each week. That not only hurts the QB's but the other players building continuity.
It's hard to get in a rhythm when you are splitting reps in a game.
It's hard to play when you know that if you have a bad series, the other guy might be going back in.
In this specific situation you have a right handed guy and a left handed guy. That's a big thing.
One likes to throw line drives, the other likes to have some arch on the ball.
One that likes to move around in the pocket and one that would like to get outside the pocket. That is hard for the OL to get used too.
The cadence will be different.
As much as they will dismiss, the locker room has their opinions. That can go bad quickly.
If I were Kelly, I'd name a starter and stick with it. If the other one transfers, so be it. The guy behind both of them is probably going to be better than either of them anyhow.