Lewin Day:
As it turns out, the www prefix largely came about due to prevailing trends on the early Internet. It had become typical to separate out different services on a domain by using subdomains. For example, a company might have FTP access on http://ftp.company.com, while the SMTP server would be accessed via the smpt.company.com subdomain. In turn, when it came to establish a server to run a World Wide Web page, network administrators followed existing convention. Thus, they would put the WWW server on the www. subdomain, creating http://www.company.com.
An interesting bit of Internet history.
➝ Source: hackaday.com

