Other possible reasons that the airframe manufacturer may have established lower engine torque operating limits than the engine manufacturer is that the rudder, vertical stabilizer, and engine mounts may not be stressed to take the extra torque of full available engine power, or you may have controllability issues with not enough rudder authority at low airspeed.

Many WWII single engine fighters would torque roll uncontrollably if the pilot applied immediate max power during a slow speed go around.

Joe