USB 2 has a single twisted wire pair, specced for moderate speed.
USB 3 replaces that with two pairs with much tighter requirements, one for transmit and one for receive. This involves a tenfold speed boost (.5Gbps to 5Gbps), with much more modern transceivers using much higher frequencies on much better wires. But it also drops the length a single passive cable can be from about 5 to 2 meters.
USB C doubled the number of pins while making the plug reversible, so they went ahead and made the special case of C-to-C cables connect to all the pins and have four pairs of wires.
But that's only a doubling from 5Gbps to 10Gbps. How are we getting up to 20 or 40? It's mostly coming from restricting cable length even further, down to 1 meter or only half a meter. But on the bright side you can get an active cable, with chips inside, that can get you back up to 1 meter or 2 meters or 60 meters. As long as you're willing to pay enough.
