Putting the hidden secret Sith cult power base on the very publicly known ancient homeworld of the Sith doesn’t really make a whole lot of sense.
It implies that at no point during their lifetimes did Luke Skywalker or Kylo Ren visit Korriban, which is silly at best.
It’s not like part of the plot involves Luke trying to track Sith assassins down or something…
Wait… 😜