Former Ohio State.head coach Woody Hayes was often quoted as saying "only three things can happen when you pass (a completion, an incompletion, and an interception) and two of them are bad." I would add an additional element in that a 3rd bad thing can happen when dropping back to pass, and that is your QB can get hit or sacked. Maybe injured.
There is no such thing as an impenetrable wall in front of your QB. The defense can always bring one more guy than you can block. An offense can't allow free runs at the QB. That is the reason a running game needs to be established. To slow down the pass rush. To have LBs step up and create spacing in the secondary. To have Safeties come up to support the run, and get big plays downfield in play action.
Football isn't played in a vacuum. One thing affects another thing, which affects something else. It's never as simple as looking at stats and saying, "Passing plays average more yards then running plays. Let's throw more and run less."