I think at GC 50, they increased the event space with the expansion into Lucas Oil, but didnt wildly increase the number of badges available. Its in their best interest to keep the attendance and available badges as close as possible, so they released more badges the next year and this year, to try to more accrurately gauge actual attendance.
I'm sure there is a practical safe attendance for the space, but its probably higher than we think.
Its a hypothesis, and I cant test it since we dont have access to those numbers. Not to mention, attendance isn't like a football game, since people are in different parts of the convention center and surrounding hotels.