Because they don't "send tickets back to Vegas." That is not how it works.

The MWC is under contractual obligation to pay for the conference allotment, not BYU. The BYU ticket office sells the tickets. If they don't sell them all, they are paid for out of the bowl money that the MWC gets from the Vegas Bowl. The MWC paid for BYU's travel costs and the rest of the money is allocated to the MWC teams and the MWC itself.

BYU more than covered the MWC ticket contract costs every year they have been in the Vegas Bowl, including last year. BYU has received and sold tickets from the other participating conference/school and sold them too.

You might want to do some research before claiming that BYU does not sell tickets for the Vegas Bowl games they have been in.

http://webcache.googleusercontent.com/search?q=cacheDOjD-5PLfoJ:www.lasvegassun.com/news/2009/dec/22/we-byu-bowl-game/+byu+vegas+bowl+2009+tickets+sold&cd=12&hl=en&ct=clnk&gl=us&client=firefox-a