Couldn't pass the physical endurance portion.
I should point out that twelve men failed as well. But that's the point. You weed out the people who can't hack it. And the Infantry Officer Course is a bear, because if you pass it, you're going to be in command of a whole lot of grunts who will surely look down at you if you cannot do what they can do.
But women don't have the physical stamina men do. They have lower muscle-mass to body-weight ratios. And they have less cardio endurance than men do. These are basic physiological facts, people. Don't believe me? Take a look at the differences between men and women on the Army Physical Fitness Test.
You want to know why women should not be in a combat arms MOS? Because women as a rule cannot sustain the kind of physical effort those jobs require. Period.