There are a lot of things our phones are capable of that we are not able to get them to do.

Even before the iPhone I had a phone with front and rear cameras and Bluetooth, it has long since been replaced and is probably sitting at the back of a drawer somewhere. If I had the ability to make it work as a Bluetooth webcam it might have had a productive second life. It was physically capable of doing this, just not software capable

The latency and bandwidth on BT does not suffice for today's expected webcam level quality.

FWIW you can use an Android phone as a web cam. Not sure what the latency is though...