This is a great example. In a practice setting you immediately reset the QB and drill the right way. In a game situation, the player repeats it three or four more times possibly getting it more ingrained, more in muscle memory, before you get a chance to even talk to him after that series is over and zero chance to practice the right way. (and you're still going against NFL talent in your own teams' defense).
He's going to end up starting this year - the OL is too poor for him not to, but this rush to throw him to the wolves is skewed way more toward negative outcomes for the longer term (bad habits, serious injuries, mental yips from being continuously pummeled, etc) then positive ones (maybe he is one of those rare few players that can self-improve in the forge of game play).