That and because of his robotic limbs he was never able to deflect lightning like most Jedi and Sith can. The Emperor kind of took advantage of that when he tried to kill Vader in Return of the Jedi.

I did some research on this. The only time Darth Vader ever used force lightning was in one instance in I believe an rpg adventure put out by Wizards of the Coast. I’d call that pretty non-canonical as Cyril says.

There’s a couple reasons why Vader may have never been able to use force lightning. One is simply that force users tend to have affinity to certain powers of the force and Vader didn’t have one for lightning. It’s not a measure of whether he was better or worse than either Dooku or Palpatine, it just wasn’t one of his ‘gifts’. Anakin seemed to be more into precognition with the side effect being his preternatural reflexes.

The second reason is simply that vader had prosthetic limbs, had he been able to use force lightning and do so, he probably would have blown his own artificial limbs off as the lightning emanates from the living body.

All the above was compared against Wookiepedia.