Is Cable still infected, couldn't they cure him? Via Ressurection, or by the brillaint minds they have at Krakoa like Sinister, or.. by Apocalypse himself?
Hickman said things like that are story opportunities.
There could be a reason for it or not one at all, but basically part of the point of HOX/POX was to give writers a plate to eat off of for years. So questions like that aren't going to be quickly answered or answered any time soon at all.