I know that RC applications, such as a drone, use PWM signals to drive the motors. This PWM signal is mostly 50 Hz (0.02 s). The pulse itself varies from 1 ms to 2 ms. So a 1 ms pulse corresponds with a minimum motor rotation and a 2 ms pulse with a maximum motor rotation. So basically the other 18 ms of the period the signal stays idle.
Why does the PWM signal have such a format? Why is the active part of the signal not spread over 1 ms and 10 ms? What is the advantage of using such small pulses?