When BYU left they tried to buoy up the old WAC. That's where they wanted to land for non FB sports. They tried to encourage UNLV and SDSU ( and perhaps others) to return to the WAC. Remember the hasty press conference announcing Nevada and Fresno State to the MWC, essentially killing the WAC?
How much of this is reality, I don't know, but some of it is, and it's their perception and the core reason for the hate from the MWC fans (at least in my experience in talking with them). They feel like we tried to take the MWC down on our way out.
I believe there is some truth to it because there was much published at the time. But again I don't know the facts. Does anyone really?