I don't think there was any way the Chargers were going 3/3 in a row on special teams. First time around, they held up Stefan Logan and stripped the ball for a TD. Second time they recovered an onside kick. I think Turner was playing the odds. There's pretty much no chance of them getting lucky/good a third time. If an onside didn't work out, Steelers have great field position, kick a field goal, game over.