All the physics and animations in the world won't teach the player AI how to play proper defense.
You'll just get good looking bad defense.
Think about it - Madden's defense is mediocre now with the "tricks" the game uses, suctions, LB jumps, "jump of my block because you hit sprint" - now take those out and make them play as per REAL physics? What happens to real defenses when they have bad logic? Yeah. You get Arizona/Denver/Dallas "Defenses".
It would get even worse, imo, unless the game learned how to play real, solid, fundamental defense and understood defensive situations. Then you'll have closer to what you see on Sunday, imo. Nice animations and physics alone <> realism, imo.