Boise St. has tried for years - remember the testifying before Congress where the BCS Schools acknowledged Boise St.’s attempts to get bigger schools to play them? They get turned down every time, with the exception of more “local” schools, like Oregon and Oregon St. Even the big Conference folks admitted as much.
No BCS school wants to play Boise St. as a non-BCS Conference opponent because the risks are high and the rewards are little. The computer gives them nothing for their efforts, and the BCS-stacked polls aren't going to boost them for winning a non-BCS Conference game that isn't spelled “N-O-T-R-E D-A-M-E.” On the other hand, those same pollsters will destroy your chances if you lose or even have to BARELY squeeze out a win.
Even for the next four years of scheduling, Boise St. has been unable to lure anyone bigger than Oregon, BYU, or Utah into a game. This is not accidental - it is a purposeful effort by the individual schools in their own best interests, and by the BCS Conferences who do things to make sure the other schools aren't taken seriously (like post them against each other in the Fiesta Bowl to minimize the victory or either team).