Copper Ethernet standards tend to be specified for over 30 metres, and go (preferably) up to 100m. That’s pretty tricky to do, you need quite thick cable with individually foil shielded pairs to achieve those kind of long distances at 10Gbps. 40 Gbps USB-C on the other hand is recommended to travel over a maximum of a metre or so of cable, with the recommended being 0.8m (2.6ft) of cable or less! Thunderbolt cables that go longer need active driver chips inside the cable in each connector to make the whole thing work.
Then there is the power issue, 10Gbps Ethernet uses significantly more than 1Gbps, so a 40GBase-T switch would be even more power hungry.
The combination of these has meant that basically most people just use fibre if they need more bandwidth.
Copper Ethernet standards tend to be specified for over 30 metres, and go (preferably) up to 100m. That’s pretty tricky to do, you need quite thick cable with individually foil shielded pairs to achieve those kind of long distances at 10Gbps. 40 Gbps USB-C on the other hand is recommended to travel over a maximum of a metre or so of cable, with the recommended being 0.8m (2.6ft) of cable or less! Thunderbolt cables that go longer need active driver chips inside the cable in each connector to make the whole thing work.
Then there is the power issue, 10Gbps Ethernet uses significantly more than 1Gbps, so a 40GBase-T switch would be even more power hungry.
The combination of these has meant that basically most people just use fibre if they need more bandwidth.