Because Port &h80 is _not_ decoded by the standard PC hardware.
There are some ISA and nowadays even PCI cards that convert the value
OUTted to that port into two 7-segment-digit-LCDisplays, buffered so
you can read it from the card, but normally no chipset actually
cares about that port. (I speak of Desktop PCs.)
I repeat: Any OUT to port &h80 is, as long as there are no special
extensions, just as well as any OUT to port &h1234 or &h4711 or
whateveryouwant as long as nothing uses it.
Since Port &h80 is now "reserved" for that POST code usage,
and it is the safest port one can use in order to delay,
Linux uses it.
If you don't want this, change it in your kernel or define
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