^ Nobody is saying a company can do only one thing. However, it does make sense to consider whether a given market and the corresponding revenue streams are of strategic importance to a particular company or not. Bing is strategically important to MS, and advertising is one component that contributes to its financing, but that revenue stream isn't strategically important the way their corporate customers and revenue are. Nadella is unlikely thinking about how to streamline the company towards becoming the best advertising business in the industry. Their corporate structures and business processes are optimized towards other goals. No company can be good at many different things. Those that try have always failed. Companies must focus on one or two things. Business types call this "focusing on core competencies". For Google, advertising is one of those core competencies. For MS it isn't. That is the underlying point. IOW, almost everything Google does is, in some way, related to improving how they target ads. That is not true at all for MS. That's why one is an advertising company while the other isn't.