The reason is that this wasn’t how Sith worked back then. This is perhaps the single good thing TROS did in making the Sith spirit canon, and I’d gladly take a retcon that improved the OT even if it makes the PT a little more silly.
I don’t think I understand this- by Sith spirit do you mean the idea that literally every spirit had transferred down the line and they were “all the Sith” inside Palpatine that he mentioned? I thought the general assumption was this wasn’t literal
But then why does Palpatine seem to gloat as he describes Darth Plagueis not being able to save himself from being killed? Shouldn’t he just be Plagueis?
Maybe because Palps killed him in his sleep and the person being killed needs to consciously transfer their spirit to a new host?
Well that confuses it a bit more- if the original point is the case, would all the Sith have built up in Plagueis only for Palpatine to not take them?
I simply saw it as Palpatine saying all of the Sith had figuratively led up to him, but he was just trying to use the transfer-power with Luke and then Rey (or Kylo) to get into a younger, healthier body.