Thus, there is a monetary cost if the advertiser succeeds. Google is just a middleman, taking a cut of those prospective sales.
The sad part of online ads is that the internet allows an advertiser, with Google's help, to potentially annoy hundreds of millions of people in order to make some small number of sales. The "solution" to this inefficiency is "targeting" and "stickiness", and that is where the whole business becomes far too intrusive and counterproductive.
In the earlier days of the internet people knew ads were not what they wanted to see on the network. I remember the first ad someone posted to Usenet. IIRC it was an immigration lawyer. Brin and Page originally said when they announced Google in 1998 that they wanted to offer an alternative to a black box web search engine that is funded by advertising.
The only thing that has changed since then is that new users are less critical, they have no idea what the internet is like without the advertising. Imagine if every household had to participate in an AC Nielson study just to watch TV. There are generations of users now that have no idea what those times were like, when people expected privacy and there were boundaries. They cannot fully appreciate what has been lost because they never experienced it to begin with. It is not too late to reclaim what is being stolen.