Blizzard are retconning Sylvanas and her past actions to an extreme with the upcoming expansion.
When she committed suicide at Icecrown originally, none of this current Shadowlands lore existed, not the new floating theme park islands, nor the mysterious “Jailer”. The place was originally just largely an amorphous, shadowy void that lacked any real substance or description, up until it became a brown, shadowy mirror of Azeroth when players had to travel there in-game. None of her actions until just now have anything to do with the story they’re currently writing, and retroactively twisting her actions to fit.
Blizzard are trying to excuse the inconsistent writing and poor characterisation of the past few expansions by trying to claim that they were actually setting this current storyline up almost a decade ago, when they’ve already admitted that in reality they just make stuff up on the fly based on what seems “cool” at the time.
This lack of communication and long-term planning is precisely why Garrosh’s planned “heroic redemption arc” was infamously scuttled purely because writing team B didn’t bother to tell team A they were turning him into a villain.