The thicker props made for glow and gas engines are built to withstand the pressure pulses of those engines. Since electric motors are so much smoother, the props can be built much thinner. That makes them require significantly less torque to push through the air, reducing your amp draw. If you were to put an electric only prop on a glow or gas engine, it would probably break after a while. If you put a glow/gas prop onto an electric motor, the amp draw would increase to the point of possibly burning up the motor or ESC and performance and flight time would suffer. Wet power uses thick props because it must; electric uses thin props because it can.