Because souls are depicted as being cognisant of their past existence; even with tormented souls who might have memory issues, it's more a psychological block.
I suppose you could argue reincarnation rules apply, and the back up is just there to give a head start in restoring the memories of their past existence; though as far as I'm aware they've done nothing to set such an idea up.
Again, the the authors didn't even know how this was supposed to work.
Context is king.
X-23's most basic surface level characteristic that any idiot should grasp: Stoicism.
I don't demand that her every minor appearance be a nuance in-depth examination of her character, but is it to much to ask she be written in Archetype?! This is storytelling 101! If you want people to stay invested in a character, you need to, at the bare minimum, write them such a way that they can plausibly be believed to be the same character!
Queen of Mutants, Mistress of Magnetism, Magnetrix and the MII, Pestilence of the Horsemen of Apocalypse, the Krakoan Oracle and creator of the Sanctus Sacrum Tournament Key, the Threshold Seed Shaper, Brood Queen of the Fall of the House of X, Lorna Sally Dane, Ph.D., of the House of M, Polaris of the X-Men
My take on the 5 and resurrection is it is the best scientific way to bring back someone... but the soul MUST be there somewhere and with a reality warper there no reason to think it's not... the waiting room provides a second non science way... that has the same physical components.
I also like it as short hand "this is how X characters come back" because lets be honest X titles have had a revolving door of death since before some of us where born.
In the real world i would be BOTH pro registration and Pro mutant rights. Xavier and Trask were both right.