The volunteer workers looked after the old people in the town.
The old people in the town were looked after by the volunteer workers.
My sister took care of my little son in the daytime.
My little son was taken care of in the daytime by my sister.
두 문장 모두 수식어구가 있는데, 수동태로 바꾸면 위치가 달라지는 이유가 뭔가요?