Here's why. Windows 98 doesn't include motherboard drivers for many motherboards with USB ports. Too bad you didn't tell more about the machine and what motherboard driver package you tried.
I have Win 98 SE, SP1 installed on my PC and when I plug in a USB device it doesn't seem to work. Is there anything I can do to 'fix' this proble,? I searched the Archives and couldn't find anything recently.