Why does the login screen always show the Host tenant instead of Default?
The Host option on the login screen typically shows up upon first login to Automation Suite, if it is changed to 'default' or whatever organization name you have, followed by a successful login, any subsequent login should show the last picked organization.
The option of logging into Host is by design in new deployments of Automation Suite (in the context of a new install, you'd have to login to the Host and setup your organization), but once you login to your organization, your browser should cache this option and present it whenever you login to the platform later.
If your browser is setup in such a way that it clears out it's site data upon exit/relaunch, then the Host tenant would show up whenever you attempt login. In such cases, you can use a bookmark to access the login with this structure: https://<auto.suite.fqdn>/default/portal_/home
This will direct you to the Default tenant as a workaround.