Don't know for certain, but I would guess the entry was created and no one bothered splitting it off into its own entry later on. (Also I'm not certain how easy such a change could be made. Can an editor just move the information or does it have to be manually reloaded?)
You can find various examples of series having multiple indicia titles hither and yon at the GCD, usually in the incomplete series.
The notes for Archie Comics Digest shows a number of indicia title changes, some of the points of change are guessed at since no one has indexed enough of the series to be certain when it changed.