'How is the keyboard interrupts always accessible at port 60?

I am in the process of learning about operating systems and bootloaders. I have found that, to read keyboard keypresses, one can use the in assembly mnemonic with port 60. This works even when writing low-level assembly programs running on a modern machine.

I was reading this article on the topic, in order to better understand this snippet:

keyhandler:
   in al, 0x60   ; get key data
   mov bl, al   ; save it
   mov byte [port60], al
 
   in al, 0x61   ; keybrd control
   mov ah, al
   or al, 0x80   ; disable bit 7
   out 0x61, al   ; send it back
   xchg ah, al   ; get original
   out 0x61, al   ; send that back
 
   mov al, 0x20   ; End of Interrupt
   out 0x20, al   ;
 
   and bl, 0x80   ; key released
   jnz done   ; don't repeat
 
   mov ax, [port60]
   mov  word [reg16], ax
   call printreg16

How does the machine know to route a keyboard plugged into, for example, an arbitrary USB connector to port 60 so it is accessible for the programmer?

assemblyiox86kernelbare-metal


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