The case was originally filed by Tina Baughman, who requested that she be allowed to use her Segway to visit the park with her eight-year-old child. Baughman, who has muscular dystrophy, was denied access with her Segway by Disneyland and sued under California and federal disability rules.
A California appeals court agreed with Disneyland, stating that the theme park had "demonstrated a Segway is an unstable two-wheeled device that could accelerate quickly, either forward or backward, and injure the rider and/or others if the rider is bumped," as cited by Wired. You can read the court's ruling in PDF form here.
The appeals court thinks Disneyland already accommodates adequate alternatives for disabled people, such as motorized scooters and wheelchairs. The Segway, it says, is just too dangerous. The appeals court acknowledged evidence of this claim submitted by Disneyland – that Hesco Bastion's CEO Jimi Heselden died when he apparently lost control of his Segway.