Just spitballing and guessing here: easier math. Look lower down at the pictures or pitchers (heh). The legs themselves aren't symmetrical. So they probably t

Just spitballing and guessing here: easier math. Look lower down at the pictures or pitchers (heh). The legs themselves aren't symmetrical. So they probably tweaked the points so that the most common range of angles to make the math easier to do. Like I said, just a guess. But with one leg bent and the other stretched out, they probably form a line close to parallel with the ground for right-handed pitchers at the point in time when the pitcher is transitioning from wind up to release.