Why does Det always wear down? Most pitchers do, but not the great ones. Is it his skinny physique? He was just over-powering and now, he is just managing. And that's his MO.
It's not wearing down. He is a two pitch pitcher (change isn't there yet) and he throws mostly fast balls. He requires more control and command and the second and third time through an order, hitters adjust more. I assume once he commands another pitch and adds it into his repertoire, he will go further and deeper into games.