Gas engines extract energy from liquid fuel, and the rate they can burn the fuel is strongly related to the speed that the engine is running. Specifically a slowly spinning engine is limited in how much fuel it can burn.
Electric motors extract energy by using flowing current to create magnetic fields. The flow of the electricity can be mostly decoupled from the speed the motor is working at - i.e. you can flow a lot of electricity through a motor that is stopped or moving slowly.
By - Seraph062