Why the sites dropdown in multi-site installation is different from the list of sites when seen full page?

Because they are not listing the same thing.

  • one is a list of sites in the multisite, aka all 4 sites
  • the other is a list of sites that you have a role on, aka 2 sites

To see all 4 sites you need a role on all sites. Being a super admin lets you browser the admin area of sites without needing a role, as the super admin flag overrides any checks.