If there is pelvic drop on left hip while on midstance, why is standing hip abduction of left better than hip abduction of the right?

If a patient presents with weakness of the right gluteus medius during mid-stance, then the left pelvis will drop and the trunk will lean towards the right. In order to strengthen the right side (gluteus medius), the patient performs closed chain exercises i.e. single leg stance on the right leg while the left performs abduction exercise (open chain exercise). In this position, while the right leg is supported on ground, it is also contracting to raise the left side pelvis in order to perform the left leg abduction thus strengthening the right gluteus medius.