Early in his career, Tim Burton stated his general dislike of sequels (via Last Movie Outpost):
“Sequels are only worth it if they give you the opportunity to do something new and interesting. It has to go beyond that, really, because you’re doing the first for the thrill of the unknown. The sequel erases all that, so you have to explore the next level, I’m not ruling anything out if the challenge is exciting.
Screenwriter Sam Hamm, who co-wrote “Batman,” had developed a script simply titled “Batman 2.” Much of this continued from the events of the first film, following the blossoming romance between Bruce Wayne and journalist Vicki Vale, as he also took on two classic Batman supervillains, Penguin and Catwoman. Hamm originally wanted to chart Harvey Dent’s downfall as he became the evil Two-Face, but the studio considered Penguin Batman’s greatest enemy after Joker.
While Hamm’s script was consistent with the darker tone of the original, he still worked towards a happy ending for the Dark Knight. It concluded with Bruce proposing to Vicki and also giving him companionship at Wayne Manor in the form of Dick Grayson, set to become Batman’s young sidekick, Robin.
It hardly sounds like the “next level” that Burton was talking about. To appease him, Warner Bros. agreed to bring in screenwriter Daniel Waters, whose work on “Heathers” Burton admired. He was tasked with completely rewriting the script to satisfy a more Burtonesque vision, and he made significant changes to Hamm’s original concept (which still received story credit). He kept Penguin and Catwoman as the main villains, but ditched Vicki Vale and created an original character, tycoon Max Shreck, to replace Two-Face. He kept Grayson, but poor Robin was later cut due to the increased budget.