Wonder Woman is a character completely based on fantasy elements without an ounce of humanity to slow her down. Wonder Woman was formed out of magic clay on a magical island to do miraculous things in Man's World, for pity's sake!
Wonder Woman has no soul to be tested, no struggle of consequence, no mighty love to call her very own, no itch to scratch, no temptation to resist, no actual cross to bear.
As she is made from mystical mud, blessed by the gods with great powers and abilities, she is much more than merely mortal.
As she was raised on Thymescira an an Amazon warrior without men, when she came to America she purchased herself a civilian identity and blended-in with other Worker Bees to be closer to her One True Love: Steve Trevor. As Trevor puts her high up on a pedestal, a kiss from her bee stung ruby red lips is as far as she ever needs to go to keep him smitten, so she remains chaste.
Even though bondage makes her vulnerable to mortal harm, she is never actually abused when she is violently captured by the most perverse of villains. Furthermore, she is able to reform her foes by magical means, to turn a bad boy into a good kid by the power of Zeus, Athena, or some other handy god.
Wonder Woman is the ultimate Princess Fantasy, but she has no discernible personality of her own. By the hair on my chinny-chin-chin, Mary Poppins is edgier than Wonder Woman!
Created by William Moulton Marston in 1941, Wonder Woman was conceived without any flaws, and that makes her impossible to be successful on the big screen. There is no way to understand her circumstances, no means to empathize with her, no reason to cheer for her. She's perfect, and perfection is the anathema of action entertainment.
Wonder Woman simply is not interesting as an individual, she is an empty vessel, a bodacious bumper sticker of beatific benevolence. Wonder Woman herself is neither flesh or female or capable of pursuing happiness. Wonder Woman might be some kind of wonderful, but who wants to see that movie?
You scratch the surface of Wonder Woman and there is nothing underneath. Wonder Woman is all surfaces and no substance: an intoxicating and wonderful surface, yes, but still just a surface. There is nothing ordinary or common about her, weak about her, lacking about her. Wonder Woman is princess to a people without men, child to a Queen who does not age, a mother who has never married and a mother who will never die.
Wonder Woman comes to America because she met Steve, but what kind of reason is that, really? Even Marston realized that this was no reason at all, so he gave Wonder Woman a mission to save the world. As Wonder Woman she can constantly save Steve's life, even race from one crazy cliffhanger to another, but her mission also prevents her from ever consummating the relationship.
Wonder Woman's mission in America is to bring peace to all people, equality to every woman and to punish criminals of every stripe. Admirable, yes, but nobody can do that. Impressive, indeed, but it's an insane goal. Wonder Woman is not insane, exactly, she's just insanely boring when you sit and think about what her mission really is.
Wonder Woman has become a staple of super hero comics and during her WWII heyday was the best-selling comic book in the world. Those days are long behind her, but through the atomic 50s, the swinging 60s, the psychedelic 70s, the Wall Street 80s, the nuclear 90s and even the Yes We Can new millennium, Wonder Woman has never gone completely away and has hardly broken a nail in the effort.
Batman has had his back broken by Bane. Superman has had his hat handed to him by Doomsday. Spider-Man has had his body taken over by Doctor Octopus. But, Wonder Woman? Not so much. Why? Because you can't break a woman of clay, you can't kill poetry in motion, you can't drop it like it's hot the way that Wonder Woman can!
But until Wonder Woman has something to lose, something real that every little girl can see makes her MORE than just The Most Perfect Princess That Ever A One There Was? Then Wonder Woman will never, ever, EVER have her own movie!