I think you're well off the mark. Before Bud Wilkinson, OU football was not yet the monster success it became, but at no point since Bud retired has attendance dropped to a few thousand people. And there have been some dismal seasons over that span.
Your suggestion that no lasting enthusiasm has been built among the fanbase by Coach Gasso's historic success (which might fairly be compared with Wilkinson's) seems, I have to say, almost petty. Why is it so hard to accept that the number of diehard OU softball fans--fans who will be there through thick and thin--has increased significantly over the past quarter-century?