there's a difference between correlation and causation, and if you can't measure/explain a direct cause-effect relationship then for technically oriented people your proposition loses credibility.
Where it doesn't work is when you have inexperienced people spending an amount insufficient to properly measure results, not implementing conversion tracking properly, using poor targeting, etc. Of course that's going to fail.
And I'll note that there are VERY technically-oriented people in the industry who seem to have no problem feeling confident that advertising works for them.
My problem is simply with people who have had a few bad experiences writing off an entire industry. All I'm asking is for a bit more evidence for such a sweeping accusation, which I think is more than a fair ask.