I tackled that question over at Football Study Hall.
The article is about Ole Miss, I could probably just as easily be talking about A&M who have also struggled to build a smashmouth culture on either side of the ball.
It's hard to have a team identity geared around running the ball down someone's throat if your main identity is about throwing the ball, protecting the QB, and getting the ball to fast skill players in space UNLESS the pass game is more directly built around the success of the run game.
For the smashmouth spread teams, for instance, play-action and RPOs serve as the main core of their passing game. For finesse spread squads like A&M or Ole Miss, the run game only needs to be capable of punishing teams that don't play the run honestly and dare them to test their mettle running on an undermanned box, or to give them a good chance in short-yardage scenarios.
I think these finesse spread teams can find ways to make to accomplish that goal without having to become full blown, smashmouth spread teams. Read all about it with the link above.