> You don't save any mechanical complication that way.
Actually, you do if you count the moving parts. A belt is always at least two pulleys and a belt. A motor is a motor. One moving part vs three.
In some cases you don't need anything at all - hybrids don't use alternators, some (like Toyota's HSD) don't even have a stepper motor for throttling and a dedicated starter motor - the two motor-generators perform this function.
Actually, you do if you count the moving parts. A belt is always at least two pulleys and a belt. A motor is a motor. One moving part vs three.
In some cases you don't need anything at all - hybrids don't use alternators, some (like Toyota's HSD) don't even have a stepper motor for throttling and a dedicated starter motor - the two motor-generators perform this function.