The "corporate" SiteAccess is available in Preview mode - which can be confusing, because it's a "special" SiteAccess. Also SIte Context does not display it, so it makes sense to make it consistent.

Steps to reproduce:
1. Login as admin
2. Go to Content -> Content Structure
3. Select preview

Result:
"Corporate" siteaccess can be selected

Expected:
"Corporate" siteaccess is not displayed.