Mostly because it's more channels in parallel. These days all of these interconnects (and high speed ether) are in the process of a bit of a convergence into w

Mostly because it's more channels in parallel. These days all of these interconnects (and high speed ether) are in the process of a bit of a convergence into what essentially just versions of raw serdes interfaces on chips - the same wires coming off the die can be 10Gb ether, PCIE, etc etc - they all just self clocked differential pairs