Seating in the rink is 7000, without seats for the floor....
Don’t know but I suspect the rental on the Broadmoor ice rink would have been very expensive (the rooms and meals are pricey). Then you have logistics issues with parking cars for the event and the guests staying at the hotel. Plus, one parking area there is where busses pick up people to take them to a tourist site, IIRC it’s Seven Falls.
What would have been cool is he could have used the football stadium at the US Air Force Academy (I’m not sure they allow outside parties to use it - just a thought). Beautiful area, maybe some of the cadets could attend, etc. When I lived in the Denver area years ago, we went to games there 1 or 2X per year. When we were visiting last summer, the groundskeeper let us go in the stadium and down on the field - very cool! Enjoyed the visit all around - beautiful chapel, hiking, decent food, nice talking to great young people.