You've made their inter school connection the only reason for including Creighton.
I disagree. It may have been part of the equation (it probably always is) but I've seen nothing to indicate it was the "only" reason.

Why go to 10 teams? Because the trend in major conferences is an 18 game conference schedule that works out fine with 10. Also it balanced the east and west divisional alignment if that would be any benefit in travel, etc.

We may think of Dayton as a different media market, but it's still in the same state; and I think that makes a difference.
St Louis and Creighton may have been a toss up, and perhaps the personal contacts made a difference.

But they weren't the "only" reason...absent further information to the contrary.