In 1991, the World Wide Web became open to the public and ushered in a new era of Internet use. In its earlier iterations, the Internet was text-based and boringly simple. It certainly did not feature GIFs of dancing hamsters.
British computer scientist Sir Tim Berners-Lee is the inventor of the World Wide Web (W3), and he began work on this now ubiquitous program in 1989 as a way to help scientists at CERN communicate. He created the first web page editor and browser, WorldWideWeb.app, in 1990. He also created three programs that continue to work as the backbone of the Internet to this day: HTML, a formatting language used to create the visual and audio of a website; URI/URL, unique addresses that correspond with specific web pages; and HTTP, an underlying protocol that allows users to exchange information.
When you type into the address bar at the top of your browser, you’re giving it a command. Entering different prefixes before a URL calls to different servers that provide different services (“mail” brings you to e-mail, and “ftp” lets you transfer files). Entering “www” means you want to contact the specific server that will send you back the requested page in all its HTML glory. The prefix "www" was never mandatory, but it traditionally served as the chosen name for such hosts. This prefix choice was mostly accidental; not even the first webpage used this prefix, and instead went by "nxoc01.cern.ch."
The reason we stopped using “www” before our URLs is simply because it’s not needed. Most people are only trying to view the HTML version of a website, so accessing the W3 has become default. It’s only when you’re looking for a different section of the webpage that you need to add something specific before the server name.