If you go back to the web as a bunch of file servers, where every URL ended in the extension type of the document you wanted, this is what you get. Then MVC frameworks said "hey, if the URL represents some semantic aspect of the View, we can show off the power of MVC by letting users swap out the view by changing the extension!" And voila, some.com/url.html for HTML and some.com/url.xml for XML and, later, some.com/url.json for JSON

Most of the big MVC frameworks offered this out of the box at some point, which made life easier before dedicated RESTful APIs became a thing.