Search engines obtain revenue from search advertising.
Search advertising is a result of the sheer number of users.
The number of users is a direct result of how good the search results are. No one is going to use a search engine that produces poor search results. In the search engine world, relevance equals money.
Relevant results = users = search advertising = revenue.
If you want higher rankings, make sure your content is the most relevant to the keywords you want to be found for.