USB 3 is a pretty plain 8b10b scheme. 10GBASE-T uses a far more complex modulation scheme which uses forward error correction, then applies a PAM-16 modulation and then packs two PAM-16 symbols into a 2D constellation of 128 symbols called DSQ128 (curiously two PAM-16 symbols would encode 256 values, but DSQ128 only contains 128).
Four pairs vs one pair already quarters the bandwidth requirements on top of that.
Is there a reason that USB isn't adopting those techniques? Too much compute required? Four pair cabling is prohibitively more expensive in this niche?
Other than the fact 10GBASE-T buyers are ready to spend a lot more per port :)