The MWC benefits from generally higher economic/population growth rates in western states, having a lot of members who are flagship universities, and significantly less pro/college sports competition than other mid-major conferences.
Keep in mind the expansion of major conferences in the past 20+ years also narrows the number of strong outsiders. Take 1998-99 when we got the last MAC at-large, all of these programs played in a 2024-25 mid-major conference:
Virginia Tech, Xavier (A10), Cincinnati, Louisville, DePaul, Marquette, Houston (C-USA), Creighton (MVC), SMU, TCU, BYU, Utah (WAC), UCF (A-Sun).