Because it's clearly simpler to have a single bus
and lose the
specialised connectors. Which PCs eventually did (long after Apple did).
Firslty whatever USB is, it is certainly not a bus.
Secondly, how is it simpler? It certainly makes the electronics a lot
more complicated (USB being a more complex protocol than the one for a
PS/2 keybord or mouse). And I don;t think it makes things much simpler
for the user. After all, there are specific conenctors for the mains
input and the video output (VGA or DVI or whatever), why is a specific
connector for the keyboard so complciated?
Additionally, isn't USB more electrically
forgiving than PS/2?
Probalgy, in that it is desiged for hot-swapping (FWIW I've hot-swapped
PS/2 keyboards nad mice with no problems, but it's not to be recomended).
But there are poleny of other interfaces that allow hot-swapping too that
could have been used. Anyway, how often dow the average user want to swap
a keyboard or mouse?
-tony