But if you're correct and online ads put off more people than they encourage to buy a product, they will eventually stop.
Couple of points:
1. There will always be people that cannot fathom AdBlock et al and will thus be forced to view ads. Most advertisers will work on the basis that a percentage of viewers will follow ads. Trouble is there is a lot of subterfuge going on with the online ads market - ads that inflate to cover your phone screen as you were about to follow a link thus generating a false statistic.
2. Google has a nice little trick whereby, when searching, a shitload of paid results come up first in the list. If the company or service you were after appears in that section then why scroll down to the real results for the link? Google would proclaim the advertising worked whereas I would state that in the absence of the paid results I'd still have gone with the same provider as they were high in the actual search results. With their tailored search results nearly every time I search these days (unless anonymising) the service/store I'm after is in both the paid and the real results. Google is just there to optimise the payoff from search and advertising however this can be achieved. PHBs will always play ball for fear of missing out.
Personally I don't care about typical page-filler ads as I block them all.