Next time you are in a waiting room flip through the magazines that are sitting there. The ads are targeted to the likely readers of those magazines.
Online targeted ads are way better.
Not to be annoying, but advertising is serious money. If you think you can do good contextual advertising you will become rich very easily. Anyone will. It's hard for me to believe that no one is doing this supposedly easy and effective thing well since all the incentives are there.
Sure, but there are a lot of ethical problems with them.
Imagine starting a service that paired individual shoppers with a passive handler to follow them around a shopping mall to build dossiers including:
* everything they pick up and look at
* what they eat in the food court
* the clothing styles and sizes they try on
* what their transportation to the mall was
* their race, gender, age, and apparent ethnicity
* etc...
Tired analogies and ridiculous strawman arguments aside, Facebook and Google are valuable because they have a valuable product in their advertising technology. What and how you use it is an entirely different issue.
Your normal usage isn't dog training or subaru oil changes. It's idle nonsense like whether Kim Kardashian is angry with Courtney Cox or whatever. There's not enough to sell you that's contextual. People have an idealized vision of what they spend time on. It's nothing like this productive stuff you're talking about.