The rule is clear.
If you have control of the football when you arm is going forward it is an incomplete pass. If you have an “empty hand” it is a fumble.
Roethlisberger is hit, but doesn’t lose control nor has an empty hand while his hand is going forward. There is slight movement, but never a loss of control.
Video is clear, they refs also ignore a blatant block in the big on the return as well.