Why not use MAVLink commands to trigger camera?

Hello all – longtime lurker, first time poster.

I’ve been doing some survey flights with my X-8, and in the process of learning (slowly) the ins and outs of mission planner, it occured to me that the Wiki and other online tutorials instruct people to trigger the camera’s shutter via the Initial Setup/Optional Hardware/Camera Gimbal path to the Shutter dropdown menu and its RC channels or Relay. Why is it that people don’t use the MAVLink command MAV_CMD_IMAGE_START_CAPTURE and its STOP_CAPTURE counterpart? Are there just not any cameras out there that respond to MAVLink commands, or is there another reason?

Many thanks for the insight.