And Plagueis learned the "secrets of DEATH" because it's just a convenient way to tell that angle of the story, albeit in a cheap and easy way, that is also kind of perplexing as to how one with such power would be killed in the first place, or need to hide out, or use a puppet Emperor if indeed Snoke is Plagueis reborn.
Hell, in the EU when Palpatine was reincarnated as a young man (effectively undoing Anakin Skywalker's entire story arc), it was just nonsense to move a familiar, and tired redemption narrative.
Honestly at this point, I am just going along for the ride, and I hope they don't re-Lucas the whole thing. So far, so good I really enjoyed TFA.