The advertiser is buying the right to put an advert in front of you, not the right to a sale. Whether they convert you is up to them, their product, their offering, etc. I think you can never buy a single product from an ad and this is still piracy.
That said, a lot of advertising is not performance/pay-per-click focused as you've described and is instead brand advertising. The point of the Coca-Cola christmas ads is not to get you to buy a coke today, it's to have a positive impression that builds over years. This sort of advertising is very hard to attribute sales to, but a good example of how you don't need to buy a product for seeing the ad to be worth something to the company.
That said, a lot of advertising is not performance/pay-per-click focused as you've described and is instead brand advertising. The point of the Coca-Cola christmas ads is not to get you to buy a coke today, it's to have a positive impression that builds over years. This sort of advertising is very hard to attribute sales to, but a good example of how you don't need to buy a product for seeing the ad to be worth something to the company.