Because the camera need a slow speed to turn, therefore, the stepping give strong torque at low speed. And we well know exactly the position of the stepping. And if we need a feedback, we can add an encoder to the motor.
The fact that the servo creat strong torque because of its gear box inside the motor. It's not the real torque from the motor. Therefore, if we also use the gear box to the stepper, we will get stronger torque than the servo. The servo hold the rotor buy continuously changed magnetic field, however, the stepper hold the rotor by constant.
And I saw in most of auto-camera, like this application, they used steppers.
yes, perhaps, for a small webcam, for example, a servo will be good. But I don't think it's good for heavier camera. Because it will vibrate with the magnetic field.