I know the AD is responsible for all athletic programs but his main responsibility is to drive success in football. That's 90% of the job. And the results on the football field have been awful. Most ADs only get one shot to hire a football coach.
There's a chance Frost turns things around this year (fingers crossed), but if the wins don't come and the recruiting continues to stink, then it'll be time to move on to the next coach. Bringing in a new AD now gives that person the opportunity to use this season to make critical assessments and possibly select a new coach.