The link is added automatically to save time and eliminate the need for event creators

to add the Hangouts link manually. This will be beneficial if the event creator forgets to

supply the link for users. 

You will also be able to add names to Hangouts video links to make it easier for people to
join the video call. The Hangout creator must have an active Google + profile for this to work.

For GAFE and GAFB accounts, admins can disable this features through Calendar Settings in 

the Admin Console.