The app was in such terrible shape at that point, both on the client side with crashes and etc, and random login issues on the server side ... I can't imagine how they thought they were going to pull that off.
My guess is the event organising team was so disconnected from the technical team it didn’t even occur to them to investigate capacity at the site. They just assumed.
They told the technical team in no unclear words that the event is happening on these dates, and if the bugs are not fixed by then, heads are going to roll.