There is a limit on how big a conference can get. That's not even concerning issues like fit, finances, etc.. Then you have to take into consideration that college presidents want to maintain collegiality among each other. Unless there is a compelling case to drastically change the numbers they won't do it. "Compelling" would include non-financial criteria, so even if a school brings in money it doesn't necessarily be a fit for an adding conference.

In any case, the Power 5 is very comfortable with 65 or 66 members. Don't expect that number to change radically.