I've read each of the codexes in turn so but I do not remember any of the craftworlds voluntarily isolating themselves without mentioning the whole 'we've been gone so long this decline to decadence is shocking.' That may be on me though as I found them horribly boring. If one of them mentions the Path, the practice of putting souls into the tears of Isha, or any other reason for their self-enforced isolation predating their evacuation efforts I missed it.