I haven't watched the video, but I can already answer the question: Because trying to extract energy from a limited (yes, limited!) source is not going to give you infinite energy. You can only get energy less than the amount which you have put into your version of the 'free' energy device contraption, be it the motor generator pair or fan-turbine pair or light-photoelectric cell or whatever the fuck has come out of idiot people's minds this time.