Comment by MrResearcher

Because DOS relied on BIOS interrupt 10h to handle I/O:

  mov si, GREETINGS_STRING
  print_loop:
    lodsb                  ; Load next byte into AL, advance SI
    cmp al, 0              ; Check for null terminator
    je done

    mov ah, 0Eh            ; BIOS teletype output
    mov bh, 0              ; Page number = 0
    mov bl, 07h            ; Light gray on black in text mode
    int 10h                ; Print character in AL

    jmp print_loop
  done:
    ...

  GREETINGS_STRING db "Hello, BIOS world!", 0

And linux doesn't rely on BIOS for output I/O, it provides TTY subsystem and then programs use devices like /dev/tty for I/O. Run $ lspci in your console: which of those devices should the kernel use for output? The kernel wouldn't know that and BIOS is no longer of any help.