The other purpose of the ad is to keep the product top of mind. Those bubbles-and-ice ads aren't to introduce you to the concept but to remind you that you want one - now.
Obviously the guy at the TV network is not going to tell Jim from Ad Co. that it's futile to advertise Pepsi because everybody knows about Pepsi. And Jim isn't going tell Pepsi's Head of Marketing that it's futile to spend money with Ad Co. because Pepsi makes up a noticeable part of Jim's annual sales bonus. The Head of Marketing would no longer have a job if they stopped advertising, so no fear they will spontaneously realise. All of them will prefer to make up stories for why it makes sense to spend more and more and more on advertising, because they all benefit. But does it actually work?