Four words: John Carter of Mars.
Mainly, 'cuase there hasn't been one to date (other than Bob Clampett's aborted JCOM toon in the 30s and a billion other 'announced' projects)
At this point, I'd be happy as a pig in horse manure with John Carter getting ANY movie treatment. Definitive can wait once we've got ONE version.
It really bugs me when overpriveledged Batman or X-Men fans complain about how their pet idea took years to become a movie. What, a whole
ten years? Boo-hoo.
John Carter of Mars has been in Development Hell, on and off, since
1932. To give some perspective here, it almost became the first full-length animated feature of all time under Bud Clampett. Later on, Ray Harryhausen tried to get the project started for years. And they wanted Tom Cruise to be John Carter, and to give some perspective here, this was back when casting Tom Cruise as a man from Mars wouldn't be quite as appropriate as it is today.