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 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.