The problem with giving pass rushers unimpeded access is that the league doesn't want 32 teams forced to play backup QBs when the starters get hurt, which they will if they're getting sacked five, six, seven times a game.
A marquee QB, in a clean pocket, arching a beautiful pass downfield—that's entertaining. A backup QB running for his life, or disappearing under a pile d-linemen, that's boring. Holding calls, too many of them, are also boring. Three-and-outs are boring, so are punts.
The league likes marquee QBs, and it likes scoring.