One thing I may not have expressed well about Gen Con is the size of the event. There were 56,614 people there. That is people, not triple-counting people who attend several days, and it probably does not include the people who showed up but were not officially attending the conference. Origins felt like a large event at 12,902 attendees; quadruple that. I heard folks spreading the rumor that the event was going to spread into the stadium next door next year, as it has already filled a convention center and spread into nearby hotels, which is a nice idea, but Gen Con would nearly be a sell-out crowd for the stadium and that would be just to pack people in seats watching something. As you might imagine, gaming takes up a bit more space than watching a game.
As Adam Smith explains, The division of labour is limited by the extent of the market, which is to say, you get more niches when you have more people. Games at Gen Con have editions listed for each, in case you insist on D&D 3.0 not 3.5 or refuse to play the revised version of Betrayal at House on the Hill. The vendors can similarly serve narrow markets, such as the booth that did green screen photo shoots for cosplayers to give them exciting, customizable backdrops. A popular game might have an entire floor, and the anime area was larger than some anime conventions.
It’s kind of a big deal. If it repeats this year’s growth, attendance will break 60,000 next year and 70,000 the next. There must be some limit to how big the event can get, but they do not seem to have found it yet.