Was there ever a definitive answer given — as in an interview with Brett Yormark or something, not just fanboard speculation.
My assumption, like most, is that they just weren't invited. But, I have also heard unsubstantiated claims that they inherit some kind of warchest of funds from the Pac12 by retaining the entity.
Being from the PNW, I have some biased perspective of course, that WSU in particular isn't any less economically relevant than some of the other BIG XII existing members — who themselves would likely be out in the cold if the whole thing had played out differently — but don't see them as a big compelling prize either.
Again, the question was whether or not there was ever any kind of quoted statement by an official individual in the know.