Optimizing content for on-page SEO is important because it allows Google to crawl the page, understand what is about, and rank it accordingly. There is another side to optimizing content which is to interest users and the users finding answers to questions they are searching for. If Google sees there is a high bounce rate on your page, they will assume that this is article is not what people are looking for when searching a specific keyword and rank you down for it. So, in reality, on-page optimization is for Google and the user because user experience and page experience are becoming a bigger ranking factor for Google now than ever before.
