hi Jerry, I have been using Depth chart Til 4th
You might try Strictly Follow Depth Chart. That gives the coach the least freedom to choose who plays. If nothing else, it will give you a baseline reading of how good your starters are relative to the backups.
As others have said, the coach will sub in players when the backup would be more effective than the starter. I can't see your players' ratings. But based on what I can see, frankly, I can't imagine that your starters are significantly better than your backups. So I don't think that's the issue. Maybe your starters have really, really good stamina. If not, your coach probably just needs to have his decision-making curtailed a bit.
One other thing: is your Foul Trouble option set to "Let Them Play" or "Sit Them"? It doesn't look like your players foul a lot, but "Sit Them" can get your backups some extra minutes if a starter happens to pick up two fouls early.
Hope this helps. Good luck.