Nothing to do with purist reasons it's just been a way for celebrities to promote whatever it is they're doing, WWE really gets nothing out of this. On top of that there are far too many of the celebrity segments in a given show. You'd figure maybe they'd try to do at least one 'big' thing with each guest host every week to add extra incentive to tune in but they really haven't for whatever reason.
If it was done well, I'd enjoy it but as it stands it's just filler. Even worse, boring filler.