Did everyone miss the part where Obi-Wan took Luke to live a peaceful life with his aunt and uncle? If his (initial) plan was to train him to fight the Empire then why did the two most powerful remaining Jedi exile themselves?

Vader's main task was to hunt down and destroy the remaining Jedi. If any rumors were to get out that the old dude on Tatooine was teaching his much younger boy toy how to move trout with his mind, Vader'd be all over that like a wampa on a tauntaun steak.