Earlier quoted context omitted.
This is incorrect. Companies do the experiments. They just don’t publish the results. Why would they? The idea that Amazon doesn’t know the ROI on their ad/marketing spend is laughable.
But then why do they keep doing laughably bad advertising?
If you're doing an $XY,000 ad campaign, it's a waste of your time and money to figure out which 50% it is.
If you're doing a $XY,000,000 ad campaign, you employ people whose job it is to figure out which 50% it is. The thing is, you usually don't go ahead and pay them to blog about it.