I would think that the area that had the feature didn't add any additional costs to the overall publication itself. I believe that it's not being featured because lately, they (probably) don't get concrete confirmations for interviews in time to publish who's going to be on the cover of the next issue.
That, or they just really don't have it together as to what they would like to feature, so it gives them some flexibility instead of being cornered into a cover subject.