> The reason is that vendors have (finally!) discovered that effectively nobody ever buys anything by clicking on a web ad

There have been a few times I've seen an ad on a website that looked like it was for something I wanted, and wanted to click it.

The problem is that I pretty much ignore the ads while I'm reading the page content, and so I only noticed these ads when I'd finished the content and clicked a link to leave the page, and my eyes are wandering while I wait for the new page to start loading. I click back to try to get back to the ad, and something else has taken over its spot. I might refresh a few times to try to get the desired ad back, but that has never worked for me.