In search, I am in research mode: in entering a query into the search box, I am announcing my intent to accept “bids” for my attention from all takers, and I’m prepared to act upon the provider of the best information in the search results to that query.
In social, I am in a very different state of mind. I expect content from my closed network, and unless I have invited a brand in by Liking or following them, their presence is very much viewed as an uninvited intrusion. It’s the loud, slightly drunk guy at the party that keeps interrupting your conversation with the interesting guy/gal.