Three-phase systems are far more than a carry-over from early electric motors. Cars, which have no legacy compatibility issues also use three phases. Three-phase power is a very good balance of simplicity of transformation and rectification with even-ness of loading.
You have to remember that alternators and generators are loading mechanical systems, so it's a bad idea to have huge cyclic variations in the load, which stresses the physical system.
Almost all modern motors use inverter circuits to generate multi-phase drive signals. Any time you see a product with a “brushless motor”, that’s what it means.
Interesting. I didn't know that. I always figured that was a method for powering (otherwise) AC motors from DC. I never realized it included multi-phase motors.
You have to remember that alternators and generators are loading mechanical systems, so it's a bad idea to have huge cyclic variations in the load, which stresses the physical system.