AWD systems can and do get used offroad pretty often. They're not quite as good as 4WD in some specific situations
The moment that you have one wheel spinning with AWD, you are stuck. One wheel in the air due to a heavily rutted fire road? Stuck. One wheel on wet ice on the road? Stuck.
AWD is great for transient traction conditions, like roads that are partially snowy with patches of exposed asphalt.