They sometimes call themselves Jedi Knights, but in the end, they are simply "warrior monks." They don't use unnecessary offensive moves, and they figh according to extremely strict rules of engagement. It is obvious that the Jedi would never use force lightning. Only in stupid EU and video games would that happen.
You can exercise restraint, and at the same time not be a sissy. And in the end, there is just no need for them to use force lightning. Can you actually imagine Obi-Wan being cornered by General Grievous, and then using force lightning to get the upper hand? It doesn't even pass the laugh test.