Removing Coruscant and Mortis seems to have been a mandate by Disney, they probably thought the Prequel imagery would upset the “hardcore fans” which is most likely also why they canned George Lucas’ scrips. Its infuriating how short sighted they were.
This doesn’t really make sense.
First of all, Mortis isn’t from the prequels, it’s from TCW. Since the Disney acquisition, they’ve had no problem using TCW stuff in other projects (not to mention TCW literally coming back later this month). Which is to say nothing of the fact that, while Mortis is gone in the final DOTF draft, Moraband has been added. Ultimately the real reason they changed it is because Rey has a different reason for going there (to find a spire that can transmit a message).
As for Coruscant becoming Remnicore, there’s plenty of explanations possible without resorting to conspiracy theories. In my mind, if the planet still looked like Coruscant, then it’s PT iconography regardless of what it’s called. If Disney had a problem with PT iconography to that extent they wouldn’t have just asked to change the name of the planet, they would have asked for a completely different kind of planet entirely.