Did you watch the game last night?  Both QB's were getting pressured quickly, with the pocket collapsing around them.  What they did different was:

1.  Look off the defenders of the pass.  Numerous times I saw Cousins look to his right then quickly throw to a wide open receiver on the left.  Siemian stares down his targets.

2.  Not consistently throw into tight coverage.  Siemian doing this happens because of #1 above.

3.  Safely get rid of the ball when the defenders got through.

Good QB's make their lines look good, just as a good line and run game helps a QB.  Difference is that both Wentz and Cousins look like they understand how to help the pass game and Siemian does not.