Generally speaking, there may be some reasons why girls cannot ride dogs:

Safety Issues: Dog Behavior and Emotions May Be Unsafe Stable, riding on a dog could cause injury to the girl.

Hygiene issues: Dogs may have parasites, bacteria or other contaminants on their bodies, and close contact with dogs may pose health risks.

Respect animals: Riding a dog may cause discomfort or stress to the dog and is not conducive to building a good relationship with the animal.