I've noticed several players that get lots of innings out of their starters, and hardly use their relievers at all (some go a full season and didn't have a single reliever accumulate 10 innings).
What settings do you use to keep the relievers on the bench and the starters in the game?
Setting your starters on F0 ensures that they'll pitch until they're exhausted (unless they get lifted for a pinch-hitter.) The downside is that they lose effectiveness as they tire, but some managers are willing to take that risk.