the reason searches are used instead of URLs has been touched upon, but in the English-speaking world we're not so used to being told specifically which search terms to use.

The reason they give the specific keyword, is to do with the difficulty of getting accurate search results with Japanese owing to its use of three native writing systems plus roman characters interchangeably and non-exclusively.
For example, a search for 'Asahi' could be typed as any of these: 朝日／あさひ／アサヒ／Asahi

The adverts give a search term which is guaranteed to bring the required page up as the #1 result instead of having to search two or three times.