Sharepoint - Site collection administrators in site setting
What you are seeing is correct. There is difference between the Site collection administrator Or Site collection owner vs Site Owner Groups.
Site collection administrator Or Site collection owner: These are the user who owns the site collection and having ownership of it. I.e. Primary Site collection admin or Secondary Site collection admin. These guys received the alerts about the site collections i.e storage quota, not used etc. These owner controlled by Central admin or Pwoershell. You can also add extra site collection administrators which is controlled via Site setting page.
Site Owner Group Site Owner groups is just a security group in SharePoint site collection with Full control on the site collection but not the owner of the Site collection or Primary or secondary Site collection Administrator. when we create a new site collection, 3 groups will automatically provisioned with "Sitename Members", "Sitename Owners" and "Sitename Visitor". This is just permission group not really admin / owner of the site collections.
If you make some body owner of the site collection then you have to make it Primary or Secondary admin from CA or powershell, if you want add additional site collection administrators then add into the Site Collection Administrators permission group via site settings of site collection.
Read this heading "Site Owners vs Site Collection administrators demystified"
What is mentioned by Waqsa is correct, you should be Site Collection Administrator to can find the Site collection administrators option within the site setting page.
But based on your above comments, you still missing the link despite you have already signed in as a site collection administrator.
Actually, it's a strange behavior, but I suspect that you are not in the Site Setting page of the top level site collection.
It's logical, the Site collection administrators option is not shown in the site setting of subsite even you are using Site collection administrator :)
So Make sure that you are already in the Site Setting of the root (Top level) site, to can find the Site Collection Administrator