Changing tactics gives a huge advantage to teams that are watching the games live. I was on vacation a week ago and I had to set my roster for 3 games to avoid missing anything. I did not have any internet to change my roster at all. Now if my opponent could have changed their lineup, doesn't that give them a huge advantage. Also imagine the coach telling this to his players
"I know we have practiced this offense for the whole week, but let's switch to an offense we haven't practiced at all and hope we do good."