The company owns the “example.com” domain name and can put what they want before it. The “www.” part (which stands for World Wide Web) was a convention for the company to put their website on, as other subdomains may be used for other services than websites. As time went on, companies started to make the “example.com” itself point to the website as it is shorter and easier to type/remember, and made the “www.example.com” redirect you to “example.com” for retrocompatibility