Although no one producing pushrod for offroad is not the reason that directly penalize the offroad performance, suspension used in a offroad car need to be a long-travel one, and the suspension need to be soft, but pushrod suspension is designed for lower the overall centre of gravity, lower the ride height and also better airflow.
While in theory there can be a long travel pushrod suspension system, it will either use up a lot of car space. Also, it will go against the advantage and the philosophy of the pushrod suspension, but cost a lot of money for engineering such thing.
And if offroad performance of the pushrod suspension is not penalized in the game, it will be OP, despite a proper offroad pushrod suspension technology in the industry is not even exist in production cars.
To sum up, if the game does not penalize offroad performance, it is not realistic, it is not what pushrod suspension actually means, and the create bad gameplay.
 A episode of Engineering Explained about the advantages of pushrod suspension