I thought they already tried that - and failed. People predicted for years that Facebook will build an ad network that will threaten Google's ad business, because it's "social". However, Facebook's ad network turned out to be a little more than a glorified traditional ad network: just showing ads to eyeballs, and only segmenting by a certain demographic and on some "interests". But that's still nowhere near the efficiency of intent-based ad networks, where people actually look for the stuff they might be interested in buying, as opposed to ads being pushed to them still mostly randomly.

You are forgetting context. Its hard to sell something to someone who is chatting.

On Google, people search stuff... Thats the place for ads. When you buy things, you search for products and reviews. You dont need social context for that .