A few questions that I think will allow us to formulate a proper response, other than “because the scholars say so”…we’re all in a position to understand, we just don’t have the background to formulate an answer:
Is there a distinction between treason and apostasy amongst classical jurists? Is such a distinction apparent by reading the Hadith? Has there ever been a case recorded in the Sunnah/Hadith of apostasy which was not committed during a time of war, for which a punishment was perscribed? If so, what was it? Are scholars invoking abbrogation, or using inference, to suggest that apostasy outside the bounds of war is identical to apostasy within?