Actually in normal and alternate law a software called integrater moves and holds the elevator to commanded position till stab trim catches up. In direct law integrater is not available. So, when stab is jammed due hydraulic or any reason it helps to get the speed to Vapp so the elevator is positioned at Vapp with stick in neutral and then put gear down. If the gear was lowered at higher speed then at Vapp in approach the nose will drop and to maintain the approach path stick will require to be held aft of neutral. This compromises side stick aft range. And in case of go around it may not be possible to raise the pitch to 15°.