It's the football stadium on the Air Force Academy, meaning there are security checkpoints at the two gates that allow access on the base. All visitors are expected to show valid ID, and may be subject to further screenings, just to get on base. The base is also north of town, so parking elsewhere and walking to the game really isn't an option.
Air Force Football draws about 20,000 fans (give or take) per game, most of them current or former military. Having military ID and a familiarity with the process helps minimize how long the security check takes, and most fans have been to the stadium multiple times, meaning they know where to go, what to do, and all the rules. And, even then, because the two gates are close to the highway, traffic quickly backs up onto the highway, slowing everything to a craw.
The Stadium Series game drew 45,000 fans (give or take). I'm assuming that most fans that attended aren't current/former military, don't have military ID, and weren't familiar with the process. So, there were delays getting fans onto the base. I'm also assuming these fans aren't familiar with the Academy, which further slowed down the process of getting everyone into the parking lot.
So, the stadium series had more than twice the fans and more delays, which exacerbated the problems we see with Air Force Football games/events. It was destined to be a **** show from the moment is was announced. Then there's also road construction on the highway and snow, which only made matters worse.
Once everyone got on the base, I'm sure there was plenty of parking/staff/etc., it's just getting there that's always a problem.