I'd probably guess it's too expensive? IIRC the original Thunderbolt spec was a fiber standard and they moved it to copper because people wanted to power stuff

I'd probably guess it's too expensive? IIRC the original Thunderbolt spec was a fiber standard and they moved it to copper because people wanted to power stuff and adding copper cabling for power + power negotiation was infeasible cost wise so they ended up with a copper only cabling solution instead.