Andy Dalton is PFF’s 2nd highest graded passer this season

I wonder what the point of finding out who the best QBs between the 20s are? Like is there a reason to take out red zone stats? It's one of the most important parts of the game. I'm not an Andy hater, he's played well at times and he's played bad at times. I'm just confused as to what the point of excluding red zone is.