The list of available simulators is dictated by three factors:
It will not show you simulators whose iOS version is prior to that of your current app's deployment target. If you want to see some recent, prior iOS simulators, make sure your app's deployment target is set accordingly.
If you go to Xcode "Preferences" - "Components", you can confirm which iOS simulators are installed on your machine.
In Xcode's "Devices" window (shift+command+2), as shown in the snapshot in your original question, you can configure particular simulator devices for your Xcode environment.