If it were truly a bus, these signaling rates would be totally impossible. Too many reflections.

In practice it's a bunch of point-to-point links, but even then the path across a PCB is pretty brutal in terms of loss. Cables are (surprisingly to me, initially!) better.

Overall though, sending some number of additional bits for error correction is often cheaper than driving the line harder to reduce the bit error rate.

Put differently: we could manage lower noise, but it would either result in a lower bitrate or (much) higher power. Instead, pick a target goodput and design for power and error correction from both sides.