Alert.turn_off using entity_id: all

Anyone have any idea why this doesn’t work? Alert seems to be the only domain that entity_id: all doesn’t work for. Oversight? Bug? Or just not supported? The turn_off service for alerts doesn’t seem to be documented at all.

service: alert.turn_off
target:
  entity_id: all

Error executing script. Invalid data for call_service at pos 1: Entity ID all is an invalid entity ID for dictionary value @ data['entity_id']