If Josh misses time to injury while Mr.Developmental 3rd rounder is still learning his way to the stadium, the rookie would be worthless to a team that is built for annual playoff appearances and while paying other producers on 2nd contracts.
It would effectively be a lost season if they were dependent on him.
If they want to bring in a prospect with potential to fill out the practice squad, fine. But, if the team stands any chance of progressing in Josh’s absence, they’d need an experienced signal caller who can identify sophisticated defenses and has leadership experience. Each year there are numerous retreads. Some never pan out and some just need a change of scenery (Darnold, Wilson, Winston, Baker, etc)