I have got a PCI USB card for the mouse and keyboard. It works in Windows with generic drivers, but does not in BIOS.
I have a P43-DS3L Gigabyte motherboard.
On-board USB is not working. It's freezing/stopping randomly, so I can't use it.
I suspect that you wanted to ask "Why doesn't it work from BIOS"?
In which case: You need drivers to use something. Your on-motherboard firmware knows precisely which hardware it shipped with and it has at least partial support for them. If you add a random third party device then you will also need to add drivers for that. Either via a ROM on the plug in card (as done with many RAID cards, extra PXE boot options on NICs etc etc), or you cannot use them until the OS has loaded*.