Still, people buy a lot of AdWords and similar, and occasionally I see a relevant ad I click. BTW ads within Facebook are usually of much better quality (for me as a reader), likely because they can correlate.more sources inside FB.
I sometimes click on ads about things related to IT and programming, if they mention something novel and important, just to be aware of the landscape, and what potential competition are pushing.
I see ads relatively rarely though, because I run uBlock Origin. So the ads I see are usually placed in context with some care, not just randomly tucked on to an unrelated webpage. Most of the ads are really poor, as I can see if I use an unprotected browser.
I've done the math on this for a few small companies. I an thoroughly convinced that this is just not true for many companies. The vast amount of sales attributed to online ad campaigns are sales that a company would have gotten anyway even without the ads.
This is a simple test. Turn off all of your ads for a year, compare against the previous. Write a blog post about it, destroy the industry.
Some time in 1980s Coca-Cola decided that they have enough of an iconic status, and they don't need as much advertising on expensive large surfaces. They prudently lowered such advertisement a bit, and checked. Shockingly, they noticed a decline in sales. They reverted to the old policy.