Maybe this is the right place to ask something that really confuses me: Why hasn't anyone really challenged Google at their core business (Adsense/Adwords)?

For all the menacing Whatsapp can pose to FB, advertisement is a much larger market, with a clear path to profitability. The problem is not simple, but not outlandish either.

Yet, candidates such as Bing and, at one time, Yahoo, continuously fail to properly serve this market.