Compulsory wearing of cycle helmets

At the moment it is not compulsory for cyclist to wear helmets when cycling in public highways. It is known that in the event of a cycling being knocked off of their bike there is a high possibility that on hitting the ground they will hit their head. Without protection this could result in damage to the skull, brain with long term or permanent injuries which could be life changing or even death. Wearing a helmet could save lives or long term disabilities.
A motor cyclist would not ride a bike without a helmet why do we let cyclist when they are just as exposed