I think you and some others are missing a subtle point here. At least, this is my guess as to how MB might be thinking.
I this era of big dollars, a formal contractual buy-out is of limited value. I mean, yes, you'll get the money if the coach leaves, but as far as a means of preventing him from being poached, it doesn't do much. If he blows up and becomes a hot commodity, the kind of places he'd leave for could easily afford whatever is in the contract. The best way to get the guy to not leave is to make it so he doesn't want to leave, and the best way to do that is to do things to make him feel like the AD has his back, and that this is the kind of place that supports him. You do that by not tying him up with a buyout, by giving him an extension in year x when basic economics might say wait until 2 or 3 years later. By doing whatever you can to say "you're the guy, we have faith in you", even before it's smart or obvious.
Our AD budget is, what, $125 million now? Buyout money (in the case of the coach doing great and leaving) is secondary. Payout money (in the case of the coach bombing and we have to fire him) is secondary. We can afford all that. I'm not advocating being careless with the budget. I'm saying you do things which may seem to not make sense economically just to develop the relationship between the coach and the school so that, if he has a chance to leave, maybe it's not easy for him. It's all about relationships, as Coach K might say. heh.