That happens in the real game too. The defense is thinking pass on 2nd and long or 3rd and long, so when the offense runs a draw play out of a 3 WR set there's usually a lot of running room. Its a bit harder to fool the D on 1st and 20 though, because the D knows that the offense has more downs to get the first, that's when you go "play-action" and beat them deep.
