Why is the minimal netboot image so damned large?

I am trying to embed a self-built netboot image into GRUB as a recovery mechanism (especially since I lug a USB drive that already is a portable non volatile installation, lugging another one just for recovering in case of screw-ups is ridicolous).

Problem is, it takes 1GB+. Removing linux-firmware brings it down to 800-900M, still terrible.

What can I actually do to bring the size down?