The amount is what an average student can expect to pay for personal costs and it is used as a tool for determining how much money families need to forecast spending. It is a figure that is required by each school that takes federal grant money for financial aid--regardless of whether the school even has an athletic program.It actually has nothing to do with athletics.
I assume BYU's is higher than many of the Pac 12 schools because they are almost all public schools whose students typically don't have to travel far for school. The fact that BYU students are often married with kids probably factors into the equation as well.
It appears schools like Texas Tech and Miss State are fudging the numbers for all their entire student population to benefit the AD. There is absolutely no reason why a student in Mississippi or Lubock should have 50 percent more out of pocket expenses as a kid in Westwood, Palo Alto, or Berkeley. On the other hand, the Financial Aid Office at Stanford would laugh the AD off the campus if the AD expected the FAO to alter numbers meant for the entire student body for the sake of promoting athletic recruiting.