13 is not a big deal. The MWC schedules 11 right now. Adding BYU and Gonzaga would add a lot of off main schedule TV match ups for TV on Mondays and Tuesdays. (plus MLK Day) that allow you to handle that odd team, and make money. The MWC has been handling 11 and an odd team for a long time.

I suspect the addition of these two schools would cause the end of the WAC, with Seattle and Grand Canyon likely moving to the WCC as replacements, forcing UMKC to beg their way into the Summit. NMSU would also go, after examining the actual landscape means the Big Sky (except Football), after trying and failing to get into other conferences.

The fallout will leave a lot of individual sports orphaned, and I can see the MWC taking NMSU Baseball (not sponsored by the Big Sky) to get a 10th and divide between Mountain (5 schools) and CA +NV (5 schools) for more sensible divisional play. Something similar in Softball with one of the orphans (RGV or UVU). What this means for the MWC is the "odd" problem is strictly Basketball, but as stated above it's no big deal right now, and with better TV match ups, will be even less of a big deal given the demand for Monday and Tuesday Night games of the week. So why add a member who would require splitting the pie another way.

I summed up the numbers of the 8 "left behind" WCC schools compared to the MWC (less SJSU who are not performing):


Air Force doesn't have DOE numbers.
Top 100 in attendance (BYU 14, SDSU 25, UMN 28, UNLV 39, Nevada 50, USU 77, Fresno St 80, Gonzaga 89 ... Boise St just misses the top 100)
All 9 of this MWC are higher than any of the left behind WCC

There is no doubt given the capacity of the MWC venues, that the attendance, already 4x that of the WCC left behinds, would increase with BYU and Gonzaga coming to town. The larger fan bases and venues assure larger crowds. The WCC schools lack that capacity in their facilities. Every WCC school is behind every MWC school (expect SJSU whom I excluded for this comparison)

Seattle would bring down the WCC average as they have only 1,404 per game and Pepperdine has the worst now at 1,619 (but that is with BYU and Gonzaga coming to town, so maybe no different). GCU would bump the WCC average up . The net impact of those two would be a jump of a few hundred.

Every metric shows that BYU and Gonzaga moving to the MWC would be an upgrade both for them and the MWC. It is likely to push the MWC to a 3 bid conference, given the depth behind Gozaga, a depth similar to the American has now (actually better according to the numbers)

... and yes as a strong Basketball advocate (hey, I coach it, my son played at Archbishop Mitty) and SJSU alumni I find this completely unacceptable by my school, and I have complained for years.