Why are rectifiers-inverters used to drive AC motors instead of using the rectified current to drive DC motors?
Because AC motors are generally much more efficient than DC motors, and since they don't require electrical contacts to the rotor, are more reliable as well.

Remember, a BLDC motor is really an AC motor with the drive circuitry built-in. At higher power levels, it makes sense to separate the control and drive circuitry from the motor itself.

Also, motors with permanent magnet (PM) rotors have limited power-handling capability. At higher power levels, AC induction motors are used, even in electric vehicles.