Why use ultrasonic beacons instead of cameras and image recognition to track where people walk? It seems like that would be more effective as you don't need cus

Why use ultrasonic beacons instead of cameras and image recognition to track where people walk? It seems like that would be more effective as you don't need customers to have a certain phone, and a certain app, and you probably already have CCTV blanketing your store (at least in Europe).