>>96751202
>Humans and Eldar are fundamentally different
That's a text to explain how souls in general work, not something that applies exclusively to humans.
Forgetting the past lives in reincarnations is part of a normal soul's behaviour, as well as it is for them to dilute back into nothingness or be created from said nothingness.

>No Eldar souls just dissolve.
Except the ones eaten by chaos, or the ones who, for whatever reason, might have chosen not to reincarnate.