[II2II]

The two reasons I can think of: to run legacy or educational operating systems. There are going to be limitations to what can be supported, but simply getting the OS to boot is part of the battle. It would also be useful for those who want to experiment with operating systems by creating their own. Yes you can do that without BIOS support, but there are many old tutorials floating around that depend upon BIOS support. The BIOS was also created as a primitive hardware compatibility layer, so it will provide basic support for things like I/O.

[Retr0id]

You get a better experience on the educational front from booting them in a VM, but it's certainly more fun to boot on real hardware.