So why are they not doing it now? There are three possible explanations: 1. They haven't thought of it. 2. They underestimate how profitable it would be. 3.

So why are they not doing it now? There are three possible explanations: 1. They haven't thought of it. 2. They underestimate how profitable it would be. 3. It would be less profitable than what they're doing now. Option 1 seems ridiculous. Option 2 is possible if Facebook is blinded by corporate inertia, or if enough people working directly on the ads feel threatened. But there are a lot of smart people working there, who stand to make a lot of money by increasing profits. So I'm going with option 3. They don't do it because spying on everyone is more profitable.