Because there is no speed reduction gears means you need a high torque motor which means high capacity batteries and motor controller.
That's done all the time with direct drive motors. What's cute about this system is the implicit continuous differential. What's not cute about this system is the complexity of creating a spinning motor, and the problem of offsetting one of the axles to reverse the direction of rotation.
The inventor's original goal was to use hydraulics, and not an electric motor; I still find the electrical version interesting, though there is probably a good reason why this system isn't used in practice (many of the issues brought up here, likely). The issue of offset, though, could be eliminated with a proper gearbox (using three 45 degree bevel gears).
I am certainly enjoying the discussion about this invention, though - which was my intent...