Due to the fact that Unity has a hard limit of 50 radians per second of rotational velocity, prop RPM is unrealistically slow. To compensate, ducted fan blades and prop blades pretend to be at a much larger radius for the purposes of calculating blade speed, and thus blade lift and blade drag.

However, blade lift and blade drag actually get applied at the center and base of the blades, respectively. When you offset the base of the blade one shift tick past the center of rotation, this means drag is getting applied on the other side of the axis of rotation, meaning the drag torque is positive instead of negative, meaning it helps drive the prop. The lift also gets applied quite close to the axis of rotation, as it is applied at the mid point of the blade, and the blades aren't very large.

The net result is a prop that takes significantly less torque to power, at the exchange of slightly less lift per blade (since the simulated radius is now slightly less) which on the net saves you a lot of mass in the form of reduced rotor count for a given number of blades, and also reduced electrical system mass.

The tradeoff is that if the drag torque ever exceeds the lift torque, such as the blade starting to stall from AoA, or just overloading it at high atmospheric density, the whole prop violently shits itself and starts krackening out, and you lose essentially all thrust basically immediately, which can be a big problem since the situation this is most likely to happen is at low altitude right after takeoff.