Generally Cimber, Garcia, Romano and Mayza only go 1 inning so lets say best case scenario your use them all to try to go all out and win this game, the offense scores 3 runs, you're up 5-4 what do you do in the 9th? Montoyo probably goes to Phelps then and we're even more frustrated when he gives up a run.
You only have so many innings from your best arms, even with the aggressive assumption you can use them twice every 3 days in a small sample that's 8 innings every 3 days from your best guys, not enough to cover the final 3 innings of 3 consecutive games. Unless you're a team like the Reds where being down 2 in the 5th is one of your better chances to win a game those 8 innings are going to be more useful elsewhere. Either tied, or ahead small any point in the game or behind small very late.
Given we have an off day Monday, had we got to the 7th inning down 1 or 2 then sure maybe you got to one of the best 4 arms, knowing if you need them all tomorrow you can still rest them Monday regardless. But I'm never using one of my best 4 guys in the 5th inning when I'm losing. Your 5th best available arm is going to have to throw an inning anyway, might as well see if he can get a scoreless inning now than go through using all your best arms only for them to blow it later, or going through using all your best arms only to lose anyway because the offense didn't score.
