Star Wars: The Force Awakens saw the introduction of Snoke, the person seemingly responsible for Kylo Ren's turn to the Dark Side. However, before fans got to know more of the Supreme Leader, he was killed off in The Last Jedi, eliminating the thought of the character having a larger purpose. That's until the big twist in The Rise of Skywalker, where it was revealed that Snoke was just a clone all along, created by Emperor Palpatine to serve as his puppet. As seen in the opening minutes of the film, there were multiple tanks filled with Snoke's clones in it, but why did Palpatine had to have so many of these clones?
While this has yet to be covered in the official Star Wars canon, as Screenrant points out, the answer could lie in the old Expanded Universe, specifically in the Dark Empire comic book series released in 1991. It was revealed that the Dark Side has "deleterious effects" on a clone body. In addition to what was mentioned in the Jedi Vs. Sith handbook, clones "are one step removed from the natural life process itself," making them more vulnerable to the effects of the Dark Side. This is also why these clones age at an "extremely accelerated rate."
Since Palpatine has been exercising his cloning abilities with the use of the Dark Side, it's safe to say that this had a huge effect on the clones. Snoke has a rather old and sickly look too, making it difficult to maintain a healthy appearance for a long time since he's a clone, which is likely the reason why the Emperor created more of these.
The resolution for these many clones lie in the non-canon content, but it'll likely make its way into canon eventually.
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