Because having a proprietary domain is important:
there are still companies that do not have their own domain, and probably do not have a site. Often they are companies that don't feel the need to be on the web, because they may only work with local activities, but still use an email address often free as @gmail.com, @libero.it and others.
Let's see what the advantages of having a domain are:
- Have a recognisable mark on your site and email
- Url and email addresses are all yours
- Professional image of your website and e-mail
- You have control of your email addresses
- No more content restrictions