The reason is that there were several batches of
4-port .318-01 based 801-PC systems shipped specifically
as multiseat ones (with two RX570 or three simpler GPUs),
and it's more reasonable to provide out-of-box support
for those in a new release instead of having to resort
to manual setups with alterator-multiseat, messing with
the installer-provided configuration by hand or giving up
(or, well, building a sideline installer images with
custom udev-conf packages).