Because Vrabel has said that when Ryan is fully ready to go he’ll be taking the starting job back, but if Levis proves to be worth the pick then why go back to Tannehill? I don’t know how Levis will perform against the Falcons defense and against the rest of the schedule, but ideally you should stick with your young guy throughout the rest of the season. Ryan has clearly lost a step and isn’t in his prime anymore, to also add on with his stats being the worst they’ve ever been. Levis might struggle at times and be good as well, but I don’t see a reason to give the job back to Tannehill. It’s about looking towards the future with Levis, letting Ryan taking the job back means it’s about giving him at least a decent send off to Vrabel I imagine.