Because ADB doesn't backup anything other than apps. Google accounts are stored with the rest of the web accounts in the device. It is a database file insider your user directory, ultimately, not part of any app.
As for security settings, the settings are scattered amongst android
, SettingsProvider
app and some files under /data/system
. Those two apps do not participate in backup and restore infrastructure of the device, so that explains why they weren't restored.
If you want to check, try taking backup of those packages individually. You would fail everytime, irrespective of device
.