Many Golden Age fans know the theme -- "Who created Batman? Bob Kane or Bill Finger -- or both?"
I think we could start full threads about how Kane screwed Bill Finger. Plain and Simple.
Simple legal issues will forever keep Bill Finger off of The Batman created by... by-line. DC has enough issues with Jerry & Joe's Estates! If they offically acknowledge Bill Finger they'd owe his estate loads of money,and then have to deal with Kane's estate over that issue.
As Bob Kane saw it (and got away with it) Bill Finger worked for his studio,and anything he contributed was "work for hire", but then,let's be honest - Bill let him get away with it!
Same reason you won't see Julius Schwartz,John Broome and Gil Kane credited for Creating/Devloping THE GREEN LANTERN on the upcomming movie - they were all work for hire. It would be nice of Julius,John and Gil Kane got a "Special Thanks" Credit - There'd be no Modern GL without them! (Bill Finger and Martin Nodell created the original concept, but the three of them more or less created the modern version from scratch)