SEO has changed a lot over the years to be a lot better not for computers, but for people. To get to the top of Google and other search engines you had to just stick a lot of keywords into a post, but this wasn't helpful for us humans when we tried to search for information, only to find sites with content that is not useful whatsoever.
Thankfully in the last 10 years all that has changed and search engines are doing a much better job of cutting spam. That has made it difficult for sites to appear at the top of search results, but so it should be. Only sites with useful information should actually appear for results.
The tactics involved in SEO are very different compared to 10 years ago. This brilliant infographic by Positionly shows us how those tactics have changed from before to now.