Ease of use.
To activate a manual diverter you must remove your hand from the loader joystick and turn a lever similar to a ball valve, put your hand back on the joystick and perform the diverted function, then remove your hand from the joystick and move the lever back, then put you hand back on the joystick. That's 4 specific manual operations.
To activate an electric diverter that has the toggle switch mounted on the joystick lever (like most installations) all you have to do is keeping your hand on the joystick, move your finger to the switch and activate it, move the joystick to perform the diverted function, then release the switch. Your hand NEVER leaves the joystick.
It's a real no brainer.