It is probably a combination of all these factors. I had a time at just under an hour, and I saw the last 4 person room get taken roughly at the 1-hour mark. After that, it seemed to be just king rooms that had a max occupancy of 2. (Uh huh, suuuuuuure)
I do know that pretty much every hotel did open rooms at insanely high prices between September and October. (I stopped checking after that) Though with the issues of last year, I wouldn't doubt that some less budget-restricted folk actually took the hotels up on those rates, which may have reduced the amount of rooms in the block at certain hotels, especially when many of those rates became cancellable. Basically it allowed people to hedge their bets.
Something I just thought about is that with the rise in attendance the past few years, the cost of hotels in the relatively close proximity have been rising as hotels keep inching their rates higher and higher since they know they will sell. I stayed at the Ramada by the airport in 2010 and had a 45 dollar rate per night, that was booked out of block. That same room is currently 85 dollars per night. I have to imagine other hotels have also increased rates, which reduces the money saved by staying on the edges of Indy.
I am that way. It got to the point where I was like: "If we are going to pay 125 for a room 5 miles away and pay for parking and have to coordinate with everyone when we are coming and going, why not just spend the extra 50-75 bucks per night (as a group) and have full access to downtown.
So the value in downtown keeps increasing as it decreases elsewhere.