It's because your Animator component has Apply Root Motion checked, which means that the character's motion is tied to their animation.
Adjusting the Walk / Run speed scale values will affect the size of the Animator's MoveSpeed float parameter, but what effect this has on the character's motion is then handled by what animations are driven by this parameter.
Adjusting the speed of the run animation itself will cause them to move faster. Alternatively, unchecking the root motion option will then allow AC to move the character directly - though you'd need to replace the animations with ones that keep the root in a fixed position.
Comments
It's because your Animator component has Apply Root Motion checked, which means that the character's motion is tied to their animation.
Adjusting the Walk / Run speed scale values will affect the size of the Animator's MoveSpeed float parameter, but what effect this has on the character's motion is then handled by what animations are driven by this parameter.
Adjusting the speed of the run animation itself will cause them to move faster. Alternatively, unchecking the root motion option will then allow AC to move the character directly - though you'd need to replace the animations with ones that keep the root in a fixed position.