Two factors not addressed:
1) Football is the "cool, place-to-be" sport at Montana. Hockey has that status at UND. At schools and communities our size, it is difficult (not impossible) to have two "in" sports that most fans feel they need to attend.
2) Bozeman and Missoula are 200+ miles apart. I am sure that there are a lot of "football fans" (who weren't originally UM fans) who have season tickets. With Fargo and GF being 70 miles apart, true FB fans have already picked to follow one or the other - or they may go to a game once in a while at both schools. I don't think there are 10,000 more fans who will readily become regular attendees at UND FB games. Obviously, an exciting, winning program will bring in a lot more people but I question if we could put 20,000 fans in the stands on a regular basis anytime soon.
I would love to be wrong with this assessment.