It's a useless feature and a source of common problems.
The function was added in 3.6:
> When URL part after scp:// or sftp:// matches one of the stored session names,
> the session is used. This way you may setup default username and/or password
> for particular host by storing them to session with the same name as the host.
That use is retained, but resolving site name in URLs for all other purposes is removed.