All Drones "Required" for registration must fly with RID. There is an exemption for recreational flyers under 250g, SO turning on the RID would be your choice really. If its "registered" you are still in compliance if your Flying for recreation...
Many private airplanes also do not have ADS-B.
Aircraft age and type: Older aircraft, especially those with simple systems, are less likely to be equipped with ADS-B.
Flight path: Aircraft flying at lower altitudes or in less-controlled...