Why you need focused content
When you are getting your office organized you probably start by filing the stuff that is easy to categorize. IRS statements go in the IRS statement file and so on. Once you have finished with the easy stuff you move on to the less intuitive items and eventually you end up with some things that you either throw out or put in a Miscellaneous file.
Google works the same way with categorizing websites. If a site is obviously all about 'pet food recalls' it is going to be easy for Google to direct 'pet food recall' traffic that way. But if a site is about pet food recalls, celebrity gossip and contains lots of unrelated affiliate content, it is going to be a bit more difficult to categorize.
This is a simple example of what the search engines look for but it is an important concept for you to apply to your website. The clearer it is to Google what your site is about, the more likely it is to show up in their search engine results.