I thought Vader cannot use force lighting because he is more machine than man?
I mean look at what Palatines electricity does to vader. Vader has no human arms either. He probably could have used force lightning as the vader with no suit In Episode III.
The real reason is because it was not in the script.
People look for logic in a series of childrens films that are pure fantasy and not real. I guess a lot of this is the EU fault because people think everything must be explained. Even George fell victim to having to explain everything uncessary in the prequels while not explaining other things.
Star Wars is Space Fantasy/ sword and sorcery. Not Science Fiction. Star Wars universe has its own logic but it happened a long time ago in a galaxy far, far away. This is Once Upon A time in a kingdom far away.
Other than the basic human story that relates nothing can be related to earth time or earth men, it is not set in the same temporal universe we live in. Denies the laws of physics and has sound in space.
If it is science fiction at all it is science fiction lite a subdivision where things like space opera and sword and planet stories get moved to, but they are closely related to fantasy which has magic and no science. The events and objects and all they use at far too fantastical and forget the science in science fiction.
Someone like David Brin would say there is a difference between sci fi and SF. SF uses real hard science and physics inside a story. The other sci fi relates to pure fantasy with science fiction trappings in which it is there to only service the plot. Usually in television or hollywood films where real science bores audiences and gets thrown out the window.
Just because star wars has spaceships and technology does not make it science fiction. Lucas claims he never intended it to be. Only Fox wanted to market it that way since they refused to market it as lucas wanted it called space fantasy, when they absolutely refused the name space opera.
To me i don't care either way its fantastic fiction and escapism just like Tolkiens lord of the rings.
To me genre restrictions are boring and more about classifying books and where to put them on shelves and to sell books than anything else.
Science bores me to death anyways if there is no good story. Hard Science Fiction almost always sucks with some exceptions like Asimov.