It doesn't really matter under what setting it's placed in the OS, but "emergency alerts" or CB is clearly network setting/service, so it's not surprising carrier can control status of this setting/service and override what you set in the phone.
Not... really? It's not the setting for whether the phone receives alerts; it's the setting for what the UI does in response (make a bunch of noise vs accept silently). The UI is very much on the user-controlled side of the phone.
