It’s light side only. Lucas explicitly justified Anakin’s presence by saying it’s because he turned back to the light side at the end, Sith are unable to do that.
You don’t want planet eaters to influence the galaxy after their dea- oops they found other villainous methods anyway. Your barbaric soul reincarnation / cloning vs my righteous light side paradise ghost, etc.

















Hint: it’s not because of costs that they won’t let you do it.