Because he rode the pine as #3.
Lance holding down the #3 spot last season could very well have nothing to do with ability/potential.
Think about it Rocky. You're managing the roster and very late in the game you are given a young QB, very unproven but loads of potential. You also have a veteran backup who knows the offense and has proven himself capable. It makes no sense to move the young, unproven new guy straight into the #2 spot. It makes far more sense to develop him. (And here's the kicker)
Especially if you never even need the backup QB to do anything more than some mop up.
There is no reason to have moved Lance up and there is no reason not to think he may win a head to head competition this year.
I would have thought such an astute and accomplished football mind like you have would have easily thought this through and come to the same very reasonable conclusion,
I'm here for you if you need any more help. Just ask.