No idea, but I remember Fergie once saying that young players are inconsistent and their game time needs to be managed well, so he would rest them. Southgate more or less played the same team except for the Belgium game, understandable as they were winning, but in hindsight some changes may have been beneficial. Even during the Croatia game in the second half he didn't see fit to change the formation. I felt that 3 central defenders against one Croatian striker was ok when we were knocking the ball around in the first half, but when the Croatians pressed in the second half, they panicked and started hitting it long. I think it would've helped to have gone to a flat back four and put an extra body in midfield which was getting overrun and stretched by Modric and co. Overall it's hard to criticise when they played well above expectations and became enjoyable to watch again...