Back in those (pre-UEFI) days it was quite easy to add GRUB to the Windows boot manager instead.

You'd wind up with a menu entry that Windows would usually leave alone, unlike its aggressive reinstallation overwriting GRUB.

Once UEFI came along, it became easier to give each OS an entire disk with no connections between them, and use the BIOS as the boot menu.

Or, y'know, just give Windows the flick and only run Linux 😉