Why is there only a 3-Phase system? Why not 6-phase, 9-phase, or some other number of phases?

A three-phase system is used because it provides constant power, more efficiency, and less cost than a single-phase system.

A three-phase system delivers three times more power than a single phase with only 50 percent more wire.

A single-phase system provides pulsating power which leads to noise and vibration, while a three-phase system provides smooth and vibration-free operation.

The efficiency of the system increases with an increase in the number of phases but also the cost of conductors and complexity to achieve higher phases (more than 3) also increases.