At that point Texas and Oklahoma were considering leaving (to the PAC12) and the only thing that got them to stay was the realization that with fewer schools, they'd split the money fewer ways.

Oversimplified version (with numbers for illustration purposes only), but if you have Texas and Oklahoma bringing in $50M each and 8 other schools bringing in $10M apiece, then the average for each school is $18M. If you do the same but instead have 10 other schools bringing in $10M, suddenly the average for each school is $16.7M. Reducing the number of slices of the pie is what convinced Texas and Oklahoma to stay at that time. And keeping Texas and Oklahoma is what convinced everyone else to stay at that time.

The time to add BYU (or another strong G5) was 2015 or so when the conference was less in flux and less motivated by immediate survival.