Not to mention, even using the remote ecobee sensors as motion triggers there is around a 5 minute delay before it updates between active/inactive status. Thereby not reliable for anything needed instantly.
The Ecobee Suite from @ storageanarchy can use the sensor data from the Ecobee thermostat along with external sensors. There is an option in the configuation. I currently use it and haven't had any issues with his suite.
You can see below it creates a sensor from the thermostat:
And I agree these sensors are not "motion" they are occupancy and it the Ecobee integration in Hubitat polls the API from Ecobee's cloud. I have mine set to poll every 3 minutes. Since the sensor is occupancy it can take anywhere from 5 to 15 minutes before a room shows unoccupied. But they do almost immediately report occupied but wont reflect it in Hubitat until it's polled.