WTH - Zones don't measure entities without GPS data

I have several person entities. One is configured using GPS data from the mobile app, and the rest use an MQTT device_tracker. I’ve linked these people to the devices created by MQTT. Even though their state correctly shows as ‘Home’, they aren’t being added to the zone count. As a result, the Home zone only shows one person at home, when it should show 4 in this example.

mqtt
  device_tracker:
    - name: "OpenWRT Billy"
      unique_id: openwrt_billy
      state_topic: "openwrt/presence/billy"
      value_template: "{{ value_json.status }}" 
      payload_home: "online"
      payload_not_home: "offline"
      json_attributes_template: "{{ value_json | tojson }}"
      source_type: "router"