Why does that matter? It’s Google’s search engine, after all! Two reasons.
The first is legal. By having a dominant position in search, Google might ultimately be responsible for going above-and-beyond to include competitors. That’s part of what the current anti-trust investigations into Google are all about. One complaint over today’s move — though likely mostly about privacy — is already being readied.
The second is about relevancy. Google’s job as a search enginehttp://searchengineland.com/search-engines-should-be-like-santa-107400 is to direct searchers to the most relevant information on the web, not just to information that Google may have an interest in.
These suggestions would be better if they included other services, and that’s the standard Google’s search results should aim for, returning the best.