Just my own personal theory. Based on that there were several big untied loose ends (vampires anyone?), many of the things said in this and the last chapter of HOLiC seem like afterthoughts to me, we never saw the staff from the cover of volume 1 and other inconsistencies throughout Tsubasa, as well as the many contradictions Tsubasa has with Cardcaptor Sakura (especially post-Tokyo).
CLAMP has said in interviews that they always decide on the ending at the same time they decide to start a new manga, so they always have a "master plan". I suspect this is the one time they didn't follow through.
