they are regimented due to limited time. positional drills are grouped; all the quarterbacks work with all the receivers. when Manning faces the scout defense for next week's opponent, Painter runs the scout offense against the first-team defense. there are literally not enough practice hours for Manning to throw every single pass. it would backlog the entire team's schedule.

Manning, as all elite quarterbacks do, puts in extra time with his receivers in the off-season, as well as before and after practice. but taking "all the practice snaps" simply means he did not sit out any plays or drills (although Caldwell curbed that habit in recent years, to protect his arm strength late in the season). regardless, no NFL team gives their back-up quarterback first-team snaps during the season.

I trust the above has thoroughly dispelled your nonsensical thread of assumption, so that you may not pursue it further and pollute the internet.