I think the anti-Missouri feeling (assuming it's not just Longhorn propaganda
) is based on the idea that they're really responsible for the Big 12 being in trouble to begin with by first floating the idea that they would be willing to jump ship and openly courting the Big Ten. While everybody else might have been upset at the Texas/Oklahoma bias, Missouri seems to have been the only ones to admit they'd be willing to jump if given the chance. Or at least they were the first to do so publicly.