It's scripted. You could be 80 overall and you'd be sixth man for a set period even if the guy starting is 70 overall. Coach logic isn't the best and just wait till you get the "bring us back" substitution glitch. Just some of the things you have to live with to play the game.
No. You are given the opportunity to talk to the GM at set intervals. Once you do you can ask for more minutes (to your GM/Team chemistry detriment).