Batman '89 was successful less for whatever incarnation of the character Burton was trying to present and more for the fact that it was the first major modern Batman movie. It wouldn't have mattered what incarnation of the character it was, people still would've lined up in droves to see it regardless. But that film has still managed to hold up somewhat over time not only because it leaps off the screen visually, but because it has a decent cast, and the right amount of levity mixed into the seriousness, which makes it enjoyable for a wider audience without ever being unforgivably corny. Fans could almost let Burton slide for going against canon by making the Joker be the one to kill Bruce's parents.
The number one reason why a Batman story does or doesn't work on film is essentially whether money is the priority over making a piece of art that will stand the test of time. The studio simply didn't give the Batman fanbase enough credit. Since the rogues gallery and their various costumes are essentially a marketing dream, it became something of a paint-by-numbers formula to maximize revenue and merchandising for each subsequent film by casting a major star in a wacky portrayal of the next villain(s) and hot actress as love interest and/or villain, neon, nipples and one-liners galore. Sure, Returns is a pretty film to look at, and the art is still incredible to this day, but the story is simply ridiculous, complete style over substance.
Post-Schumacher, the studio finally wised up and realized that story is what makes the character so unique, awesome and beloved. It could also be a matter of public taste in that audiences today have grown to become more interested in psychological aspects of certain characters, and Bruce/Batman and his companions and rogues happens to lend themselves extremely well to those types of stories. You can't have this crime drama, murder mystery, detective story, psychological character study, and then suddenly have a mutant or someone with super powers, or even a character in a bright green or purple costume, or fishbowl on his head breaking that tone, it doesn't work.
They could've gone any one of several different ways with a standalone Joker film, and the route they decided to take (which couldn't be any more grounded in reality i.e. no acid bath or permasmile) resulted in not just one of the best comic book movies of all time, but one of the most acclaimed films of all-time period. If that doesn't indicate for you what style or incarnation of these characters the GA would prefer to see, nothing will.
