When it comes to the care and feeding of rookie quarterbacks, NFL coaches are clueless. They can beat the Tampa 2, they can create endless stunts and blitzes, they can detail the intricacies of the spread offense, but they can’t figure out how to handle a rookie QB. NFL teams spend millions of dollars on wildly successful college QBs and then they turn them over to their coaches and cross their fingers.
You get better at football by playing football. There isn’t enough practice time to fully develop a QB if you start him and give him every practice rep, let alone with the massively limited work you can do if you if he’s the backup.
Jordan Love looked like a rookie last year. Mahomes lost playoff games because he didn’t know how to read a defense after wasting a year on the bench.
Either a guy learns from his experiences or he doesn’t. But not playing doesn’t give him a path to the learning that’s required to play QB at a high level.