Who to focus on? Search engines or the reader?

In search engine optimization content is the king. SEO copywriting thus gains importance. But who is the target audience- the reader or search engines who determine whether the content should be read by the people or not? The answer lies in the question itself. It is the search engines who determine the relevancy of the keywords in the content and decide the position of the page or the site in the results page. So, I believe SEO copywriting is targeted more on search engines.