The DD was a really good idea from Nintendo, but using floppy disks instead of just regular CDs was a big oversight. Classic Nintendo bending over dollars to pick up pennies in an effort to prevent piracy.
DD floppys were writable but I am pretty sure they didn't fit into a standard floppy drive either. Sure, drives capable of writing to CDs may have been more expensive at the time, but at least it wasn't specialized equipment and you could use it for other stuff as well.
