I think the best explanation they gave is that Brewer has been hit too many times. He talked about the 2019 Big 12 championship game, where OU got a big hit in on a sack, and said that Brewer hasn't been the same since that hit. On top of that, Baylor had O line issues last year, so Brewer took a lot of punishment.

They suspect that his body has just taken too much punishment. I suspect he went to Utah with the idea they had a strong offensive line and could protect him from taking those hits. With Utah's O line being found wanting, he just can't keep taking a beating week in and week out.