From HuffPost UK:
“[…] You’ve got questions, and “The Rise of Skywalker” editor Maryann Brandon has answers. […]
Why we don’t hear many details about how Palpatine survived.
The opening scenes with Palpatine (Ian McDiarmid) were “tricky” in terms of how much of the character’s backstory to explain, how much to show of him and what he wanted, Brandon explained.
“It was kind of a delicate balance and went back and forth a lot about how much we wanted to reveal,” she said. “Some scenes changed quite a bit, the way that we wanted to present it to the audience. In the end, we ended up showing a lot less of it than we started with.”
There was originally “a little more information about it, what was keeping [Palpatine] alive,” but, Brandon said, “it seemed to go off topic.”
“There was so much information in the film and so many characters that we wanted to have an audience concentrate on. I think we felt we didn’t want to clutter the film up with things you didn’t need to know,” she said. […]”