It is because whether the player is stopped from being able to play the ball is

One of the three key considerations.

1. Is the player in an offside position;
2. If so is he directly obstructing the keepers line of sight to the ball;
3. If so has it prevented the keeper from being able to play the ball.

VAR only looked at point 1 as far as I can tell.

Being in an offside position is not in itself an offence.

Posted By: Jim, Aug 29, 19:43:14