how to make a cnc machine with servos as drivers?

Unlikely to have the kind of torque a CNC mill would need.
Agreed. Unless you're talking about industrial-size servos (which do exist, but aren't cheap).
I suppose if you want to get "picky", then a CNC machine is itself a set of servos (motor+feedback+amplifier).....

True, in the general sense of servomechanism.