Like someone else posted, it's not like the Reds have been more successful in recent years than the Bengals. There's a lot of parallels to be honest. In 2010 the Reds beat up on bad teams and lost to good teams, then had an early exit in the playoffs. In 2011 that's exactly what the Bengals did. Neither franchise has had any postseason success to speak of for quite some time.
Why is Marvin the coach? If you ask me it's because he's about as good as we have been able to get for a while. Just like big name free agent players, big name coaches don't exactly have working for Mike Brown high on their list of things to do.
With all of the really bad, it's still going in the right direction right now. We're missing talent at certain positions and it's hurting us. We're also inexperienced at spots which is also hurting us. Prime example is what Dick Lebeau did to Jay Gruden last night...just outclassed him from a coaching perspective.
Ideally the team continues to mature and either Gruden or Zimmer takes over the HC job while Marvin moves to a FO position where he can be here to put the team together. For all of his faults you cannot say Marvin hasn't done a good job at raising the level of talent all over the team. Whether or not this happens is anyone's guess, but that would be my hope.