I had the exact same scenario as you the same issue 2 seasons ago in div IV. I blew out so many games that all my starters would only get around 25-30 min a game.
Having said that, it is only one factor. The other factor is like the other poster said, he only played 18 games instead of 22. Games played also play a significant factor. From that same season that I experienced, my best player averaged better numbers across the board (despite playing significantly less minutes than the guy that won) but he also only played 18 games instead of the other guy's 22.
To be honest, i think games played is given too much weighting. Since a slight injury pretty much rules you out of the running for the award