Cast members wear costumes sized in the 70s.
Over the years, clothing sizes in the real world have changed, especially for women’s wear. As people have grown larger, sizes have grown with them. A small today is closer to a large from the 1970s. In most places, workwear has also adjusted, but not at Disney. Costume-makers at Disney, as is the case with any stage environment, use the same templates they’ve been using for decades, especially with costumes. To receive uniforms that fit, cast members have to order clothes in larger sizes than they’re accustomed.