No one has the data for both sides of the equation. Google dominates search advertising, Amazon dominates online buying. If those companies merged, one company would have all the data needed to use deep learning to take all our money. They'd be able to distinguish products that, once purchased, means the buyer won't buy again for years, and items that are regularly bought, and they'd have the timing between seeing ads and buying. It wouldn't be perfect, because some people would buy elsewhere, but it might be frighteningly effective.