I've always thought (anecdotally - no substantiating evidence) that advertising on the internet, which is much different that advertising in a magazine or billboard, is probably a loss leader or close to it. The real value for the product manufacturer is the data they steal from you. In all honesty, I can't think of a product or service I've purchased that was based on an advertisement. 99.999% of the time, I know what I need or have a really good idea, and will research it on the internet extensively, depending on value, and make my purchase based on my research. It also could be that I have made it a concerted effort to never see any online advertisements on my network, so maybe I am not as affected as those who see ads in every square inch of their monitor every day, like they're on a porn site.
Network so tight I call it virgin. /s