Each member of the MW plays 8 conference games each year. They play the 5 other teams in their division and then 3 cross over games. BYU this season plays 6 Mountain West teams. Outside of Boise, the Mountain West teams are the bottom of the conference. Utah State was picked to finish last in their division while San Jose and Fresno were picked at the bottom of their divisions. There are 2 other G5 teams on the schedule. East Carolina was picked to finish 2nd to last in the American. UMass is an Independent that recently moved to FBS and couldn't quite hack it as a member of the MAC.
If you replace those 8 games with a MW conference schedule then you get a slight upgrade. It may not be massive but it is better and you are also eligible for a Conference Championship. Maybe that's not the most important thing to everyone but it does give players something to play for late in the season and can add some excitement. You like playing Boise now, could you imagine a late season game against them to determine the Division champion?
That still allows games like Utah, LSU and Wisconsin to happen. You are simply replacing a mostly MW G5 schedule with a full MW schedule and a possible CCG.