Indianapolis itself would probably not be able to handle the 80k+ fans for a football game in addition to the Gen Con attendees. It would not be in their best interest to have both in town on the same weekend. If you thought housing was difficult now, imagine the added problems an additional 80k+ football fans all converging on the city at the same time would be. You would have angry fans from both groups all over town. I am sure that Indianapolis does not want a reputation of not being EVENT FRIENDLY. This is why the city works with the NFL (as does EVERY other NFL city) to make sure that it is able to handle any major event that comes its way. Gen Con is scheduled 5+ years in advance, so Indianapolis will work with the NFL to make sure that the Colts are not scheduled during the Gen Con weekend.