Actually, I know it may not be intuitive, but helicopters fly like birds. Unlike fixed wing aircraft, helicopters manage lift, direction and thrust with their blades, as birds do to their wings. While airplanes handle lift with their wings (and other lifting areas), thrust with the motor and direction with flight control surfaces (e.g. ailerons).
If your question is why don’t we have airplanes which flap their wings: basically we don’t have any kind of material which could handle that kind of forces. Additionally, as others have said, it would be very inefficient.
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