It's been a more recent development however, as Jamie Delano was doing his best work on Hellblazer. That was before DC decided that John Constantine should be a character who appeals to fans of, say, Sabrina the Teenage Witch, rather than, say, Ramsey Campbell.
How many incarnations of Papa Midnite have we seen now? Just because he first appeared in issue #2 of Hellblazer, he must considered one of those recurring characters whose legacy must be kept going from version to version, much like a Marvel Universe character like Blob (from X-Men) or Gladiator (from DD). They appeared so early in the titles, they must be important to the mythos and must keep being used from series to series, whether there's a good story for said character or not.
I'm not reading this new series, and heavily disagree on the Milligan (but you know that already), however I will say that I felt annoyed how Ennis killed Midnite off so damn quickly back in the day.