it's really very simple: people posted I-Ds with the assurance that they
would be retired after six months. it's not reasonable for IETF to
violate that assurance without permission.
so if IETF wants to make old drafts publically available (and I agree
this could be a useful thing), it really should get permission from the
authors. or at least notify them and give authors the chance to say
"please do not make my old documents publically accessible".
it would also be reasonable to allow authors to specify, when submitting
a new I-D, whether the draft should be made available after expiration.