The idea for the PC-9N was to make a simple, back to basics case (excluding the rail motherboard mounting), therefore we did not want to go overboard with hard drive bays. While it is true that we have mini-ITX cases with more HDD bays than the PC-9N (namely the PC-Q25 and PC-Q18), this was not the target we were going for with this case.

Not to answer a question with a question, but how many drives do you usually use in a mid tower case?