This is all measured and not really estimated. If you think that any substantial chunk of that 484Billion is being done 'stupidly' then you're just making presumptuous incorrect guesses without knowing much about the industry.

Revenue (sales) - Investment (total costs) = ROI There is ROAS which similiar: Revenue - Ad Spend = ROAS You can measure things in more detail like CPA (cost per acquisition) to work out how much ad spend you have per sale, again this is a measurement not an estimation.

Where previously there was mass advertisements to millions of people like TV or radio ads which were only affordable to large companies. Advertisers now can target the exact type of person they're trying to market to for their niche which is a lot cheaper and so more accessible to smaller businesses. To me that makes business sense to do if I can optimise to the right ROI, and nothing to do with FOMO or vague thinking.