The difference is John Carter was about a completely erroneous, outdated fictional interpretation of Mars, was based on books written almost a century ago, and on a series that *never* had anything more than a very small but very loyal group of niche followers....and then the movie proceeded to crap all over the beloved canon of that small but very loyal group of niche followers.
And everyone needs to just own up to the fact that the general audiences don't know ANY of the remaining Marvel properties, so the odds of success of ANY Marvel Studios movie henceforth will have absolutely nothing to do with how "well-known" the characters are.....because they aren't. Well-known. NONE of them....Black Panther, Ms. Marvel, Ant-Man, Dr. Strange, Luke Cage, Iron Fist, The Inhumans, The Runaways, or the Guardians of the Galaxy.
It's all a crapshoot after The Avengers.