Why are we prevented from plugging an External USB camera into an iPhone to use as a camera video source? If I choose to carry the phone on my belt or in a zippered chest pocket, and USB-cable it to a helmet cam on my head, why is this disabled and prevented from our choice?

I am certainly not interested in wearing my expensive (to me) iPhone on my helmet while in the water. And yes, my reason requires seeing live video on the iPhone. I'm not talking about swapping/copying files later, and I even feel streaming over wireless is not (latent) fast enough.

Has anyone run into this block yet? Can you describe it a bit to me? Why do you feel Apple has locked us out?