We uses 50 Hz because England has control over India and England uses 50 Hz frequency because It is a sweet point of other frequencies, Lowering the frequency will Increase Size and weight of transmission line and Increase in frequency Increases Losses. So in the time of Second World war Requirement of copper is increase for making Ammo. Hence they can not use Lower frequencies as the cost increases and Transmission losses can not be bare by Increasing frequencies hence Started using 50Hz. This is Trade off between Transmission loss and Transmission cost.
