Football fans watch their teams live. This is why advertisers are flocking to college football and the NFL, because everything else just gets DVR'd and watched without commercials. The BYUtv replays/on-demand online serve two purposes really:

1-help those who are out of the country
2-satisfy obsessed fans' need to re-watch games over and over

The number of people who tune in for the first time to watch a BYUtv replay is very low. The problem with Fox from a BYU perspective is that, other than FX, most of their channels are regional. BYUtv would be necessary for fans from around the country to actually see the game.

There are very few programs with such a high percentage of their fans outside of their "regional" footprint. All sports broadcasting is based on regional footprints, however BYU is the exception. If Fox can't see the financial benefits of a national fanbase by conceding replay rights, that is not great business on their part.