Oddly enough, it doesn’t use Bluetooth. It’s a light sensor on the door. The phone actually flashes the screen at the light sensor to program it. I’m sure by being a native app it gives them more control over the screen but still….
Does the app work when offline? In that case it kinda makes sense since farms tend to be in areas with no cell service and a web page won't work with no service. The lack of Bluetooth maybe they just don't want to troubleshoot with people who might not be able to call to troubleshoot while being near the device.