I'm sure money played a factor, but fact of the matter is that there is a difference in enrollment of 593 spread out between 24 schools in 7A. 10 in 6A, 8 in 5A, 4 in 4A, 3 in 3A, so on. Like I said, parabolic. 7A had to separate because they were bigger than the rest. You could almost say 7A should be even smaller, you're starting to get the same consolidation you see in MAIS.
For reference, Georgia only has 6A. They didn't have the need to separate into another division.
I think bigger playoffs are more about money than the divisions. That's more about sheer safety and at least SOME level of peer competition.