The high profile games don't always sell out. The Miami Beach bowl, the Mizzou game and the West Virginia game are prime recent examples. This horde of traveling BYU fans is a fallacy. Look at the TV ratings. Some 10 year old African kid might be a fan, but we don't even sell out at home against a Utah!
Let me know the next time a Notre Dame game doesn't sell out, even though most of their fans have not been to the Vatican. There are literally hundreds of large and small Catholic colleges and universities playing football. If your an LDS fan, it's BYU or nothing. If there are so many LDS football fans out there, why has the Church shut down almost all the programs?