Brushing, flossing, and mouthwash doesn't kill all of the bacteria in your mouth. Your entire mouth is coated with a biofilm... and after cleaning, your mouth gets recolonized by bacteria from between your teeth, beneath the gums, plaque, and other small crevices in your mouth.
Probably, but the difference I see is that single application of this product is enough (as opposed to buying mouthwash and other stuff that's often discussed here like toothpaste with Novamin for the rest of your life).