First and most obviously, Andrelton Simmons’ pop to left field was too deep to be calling an infield-fly rule on. That wasn’t a routine play for Pete Kozma. It certainly wasn’t a ball any shortstop would have thought of dropping in an effort to get a double play. It wasn’t an infield fly.
That said, here’s my theory: the only reason that ball dropped was because left-field umpire Sam Holbrook yelled “infield fly!” Kozma didn’t lose the ball in the lights. He peeled off at the last second because someone called him off. It wasn’t left fielder Matt Holliday, who was as shocked as anyone that the ball fell in. Perhaps it was a fan with a particularly strong set of lungs, but I doubt it. The park was plenty noisy at the time, and Kozma wasn’t at all close to the stands.
I think Holbrook yelled before he put his hand up and Kozma thought Holliday was calling him off. That would also be the best explanation for the umpires not reversing the call. If they thought the only reason the ball dropped in was because Kozma heard Holbrook yell, then it certainly wouldn’t have been fair to put Simmons on first.
Anyway, that’s my theory. Hopefully crew chief Jeff Kellogg will be open to discussing it after the game.