Better return on investment as compared to normal ads

When you invest money for promoting your brand and getting thousands of visitors via paid ad, just 2 percent of those visitors are likely to convert into
sales. But a thousand clicks from SEO can result in 4 percent of those visitors being converted into sales, which lead you to have a better return on investment. This higher conversion rate is just one of the main advantages of SEO that cannot be attained by any other type of marketing.
To your website, Google just get those people who actually look for you. These are the visitors actually searching for your product. Ads on the other hand, invite all, so a lot of “wrong” people might click on an ad mistakenly. A hit from Google is more precious than a hit from an ad.