Authorize works after setting validator

Why FormRequest sets validator and only than checks user authorization

public function validate()
{
        $this->prepareForValidation();

        $instance = $this->getValidatorInstance();

        if (! $this->passesAuthorization()) {
            $this->failedAuthorization();
        } elseif (! $instance->passes()) {
            $this->failedValidation($instance);
        }
}