Good question. He obviously wanted to bring in Núñez for Sørensen to increase our attacking power at home, but this was well countered by Mowbray. The problem was more than the tactical change though, as the players failed to take advantage of the free man up front as the passing wasn't good enough or quick enough.
Which raises the further question of why he felt it necessary to "increase our attacking power at home". From what Angus Gunn said afterwards, they hadn't expected Sunderland to press as they did. It sounds as if they had prepared for Sunderland to sit back and were knocked completely out of stride when they didn't.