The AAC would’ve been a decent option had they not grown so fast. You can’t have teams with no fan bases like Tulsa or Tulane in your conference, even if they have decent on-field success or if they bring desired markets. Teams like ECU & Fresno State, which can put 40k+ in the stands every week have much more value.
Most of the SEC programs are located in undesirable markets, but viewers & recruits are won over by the passion & pageantry. That’s why you set a benchmark where only teams that average, say, 30k in attendance are even considered for membership.