The reason is that at the turn of the with century the Iowa team had a black football player by the name of Archie Alexander who Missouri demanded not be brought to Missouri for the game. Missouri threats ed riots if the black player was allowed to clme and play.
Iowa succumbed to pressure and did not bring their star player. But afterwards the coach stated he would never play Missouri again. And Iowa since 1918 has never played Missouri again.
Today not much has changed in Missouri. Shame racism.