I suspect it is the following reasons:
1. He can't block very well in pass protection. From what I have seen, he isn't very good at it.
2. Coaches/Jerruh think Barber is a critical 'team leader' and want him on the field. And obviously, he is a better blocker than Choice.
3. Coaches think Choice is more prone to turn the ball over.
I don't think he is in the dog house....just doesn't seem like something Garrett would do. In terms of pure running ability, there is absolutely no doubt in my mind that Choice is better than Barber.
I would play Choice more, but I guess reasons 1-3 are important drivers for Jerruh and Garrett.