There was a freakonomics podcast recently about advertising (online and traditional). No one can actually prove it has any ROI at all. No one is willing to run the experiments necessary. In the few cases of natural experiments, where ads got turned off for some people by accident, there was no change in buying behavior. https://freakonomics.com/podcast/advertising-part-1/ https://freakonomics.com/podcast/advertising-…
I suspect that if our browser isn't blocking ads then our brain is. It's complete conjecture, but I assume that adblockers eliminate this cognitive load explaining a portion of why they became successful before they were necessary for security/malvertising.