The selection of airfoil depends on many factors, and often ease of manufacture dominates, especially for small, light inexpensive helos or homebuilts. It an also be the fact that the airfoil was approved 50 years ago when it was state of the art , and re qualifying a new, better airfoil is expensive, time consuming and only a few percent improvement.
Old helos used the symetrical NACA 0012 airfoil, which was kind, easy to make and efficient. More modern ones use drooped nose airfoils like the Sikorsky SC 1095 or the Boeing BV 7 which are more efficient, especially at high lift near blade stall.
The blade pitching moment is an issue, where the symetrical airfoils don't take any force on the pitch links to select a new angle of attack, so unbosted controls are OK. New airfoils generally need to be muscled into position, so a boosted control system is often needed to get the increased efficiency (thus the gross weight gained with the new airfoil could be cancelled by the weght of the hydraulics!)