BIG are happy with 14. The SEC were happy with 14 members, but then had the opportunity to make more money with 16 so they are taking it.
Did you notice the motivation there for the SEC? They will be making more money. No conference will expand unless it makes them more money. No conference is going to go to 16 unless it makes them more money. So, again, they aren't going to 16 just for the sake of going to 16.