For example, it is practically impossible to create FireWire adapters over USB because FireWire needs DMA which USB doesn't provide. Is there a similar blocking technical reason as to why no 10 gigabit Ethernet adapters appeared using the USB C port (but not Thunderbolt)? GigE over USB 3.1 Gen 1 (and even USB 2.0) is everywhere, is there something in the 802.3an standard that blocks this?

I understand the economic situation here, that the more expensive laptops with USB C also are Thunderbolt 3 capable and it's somewhat unlikely the owners of cheap ones will want a 10 GbE adapter. This question, however, is about the technical reasons (as the economic argument can be countered with USB C being much cheaper than Thunderbolt 3 but again, let's leave that argument for different sites).