USB was designed to replace various PC perhiperal interfaces including things like keyboards and mice. The priorities included low cost, low power consumption and passing high priority traffic with low latency. Support for long cable lengths was not a priority. So on the protocol side they went for a simple half duplex "speak when you are spoken to" protocol with small packet sizes. On the hardware side they went for a non-isolated differential signaling system which took some shortcuts on termination.
USB gradually evolved to add higher speeds and full duplex but longer distance was never a design goal.
Ethernet (in it's early form) had a different set of design criteria. It was designed as a local area network standard, no one station was a master and they went for a carrier sense multiple access system with collision detection. To ensure the collision detection worked properly they put restrictions on both minium packet size and the total size of the network. The physical layer was designed with far more careful termination to ensure signal integrity was maintained even over long runs. There was an isolation barrier to protect against issues caused by ground potential differences in long runs (twisted pair ethernet uses transformers, I belive coax ethernet used optoisolators and DC to DC converters)
CSMA/CD worked fine on small 10Mbps LANs but it started to show the strain as speeds increased and networks got bigger. Bridges (later known as switches) were introduced allowing networks to be split into multiple collision domains. This allowed networks to be made bigger than the limits imposed by CSMA/CD and also allowed multiple speeds to coexist.
Later Ethernet moved away from CSMA/CD1 and hubs towards point to point full duplex links and switches. This allows high speed long distance links as packets can never collide with each other.
There is a price to pay for all of this though, the physical layers that can work over long distances require considerably more power and considerablly more expensive transceivers than those that are only designed to work over short range. Data buffers, at the end devices have to be much bigger to deal with potentially long acknowledgement time and potential packet loss. Switches are relatively complex devices often including substantial ammounts of buffer memory. Prioritisation requires every switch in the chain has to be aware of the prioritisation information.
1 At 10Mbps hubs and CSMA/CD were pretty much universal. Early 100Mbps deployments also heavilly used hubs and CSMA/CD. Later 100Mbps networks tended to use full duplex links and switches. At gigabit the standards included CSMA/CD and hubs but i've never heard of anyone actually selling a gigabit hub. At 10 gigabit and above CSMA/CD and hub support doesn't exist at all.
