Answer: The information on the web page that's not visible is important since it tells the browser what to do. It may not be important to the viewer but it still needs to be put inside the code for it to function properly.
Another reason that metadata is needed is because it controls how people see it. For example, the "charset" shows what type of alphabet you're using on your webpage. Descriptions and keywords help the browser identify your webpage and know what's on it. The viewport can control how the webpage is viewed on the browser and on other devices, such as phones and tablets. Metadata can be used for this and much more.