I'm going to guess that some stuff might be there, if for no other reason than to support the bootup process for computers that use the classic BIOS which start

I'm going to guess that some stuff might be there, if for no other reason than to support the bootup process for computers that use the classic BIOS which starts at 16bit real mode. Although considering that 32bit Windows can still run 16bit code, i guess they also need to be able to compile the 16bit-to-32bit bridge code so this is probably another reason why the 16bit stuff exist.