Why can't modern video cameras be used for live streaming without a capture card? I'm just curious what the physical limitation is now-a-days that connectors like USB-C and thunderbolt exist. In the past I thought the issue was that the encodings that video cameras put out (probably mostly some variant of h.264 or h.265) required more throughput than USB could offer but now that doesn't really seem to be the case. What's the issue?
I am not 100% sure but I think that there is a need for a minimal system managing the Internet Protocol in order to enable streaming. So it means there would be a need for a CPU, an OS, and a interface to setup all the related settings to the camera too.

I think the computing power needed for video compression would be possible thanks to a recent processor like the one embedded in smartphone. And of course the rate is no longer a problem for new connections. USB-C would even be able to stream raw video 4K 60fps = 12Gbps. Which is fine for be DisplayPort 1.2a available on USB-C