when SMART is disabled smartctl will exit0 but contain no smart_status which means default values get used and the device is considered invalid. since we don't know what the status is in this situation we'll consider the entire data set invalid and thereby hide the device.
with the growing amount of potentially discarded (but present) data blobs it might soon make sense to think about rendering invalid devices in the KCM with an unknown state so people at least can find out that their drives aren't being monitored
BUG: 435699 FIXED-IN: 5.22.0