Not an apples to apples comparison really. Amazon owns the entire user journey on its platform, which the "ads" are an integral part of. They are not analogous to Google showing you ads in banners and searches for target pages it doesn't own, on platforms it doesn't own. If you want to compare Google to those who actually advertise with the scatter-shot approach, you compare them with traditional advertising providers - ad spaces on TV & radio channels, billboard companies etc. That'd be a fair comparison because Google is also essentially a seller of ad spaces it "rents" from other websites - just in this case those ad spaces can simultaneously show different advertisements for different clients to each user, based on that user's best-match profile. It's a no-brainer that Google's approach will yield more leads.