Because you did not disable RAID in BIOS. I've installed XP on more than 10 nf3-nf4 board of different brand and I never had to specify any drivers, unless I wanted to set up a RAID array.
Gigabyte motherboard were notorious for shipping with RAID enabled for SATA connectors. And RAID is no use with single drive on these board..
Enabling RAID prevent the main BIOS to list the drive to the installer. It pass the controller to be used by the RAID bios, and in this case, the installer wouldnt see the drive, without drivers.