I have had this problem as well. Just in my last game my PG was set as starter, sub, and reserve but played only 35 minutes in a 70 point blow out.
That's because you used 10 players. In a blow-out, all the players will be given the chance to play, even if that means replacing a player supposed to play the full match. Put 9 players and you'll be fine.
I'm not sure if all players are necessarily given the chance to play as much as any starter that can possibly be sent to the bench will be. Functionally, it's the same unless someone's really anxious about the minutes for their 11th and 12th player, though.