Not utilizing full disc capacity - The Strangers

[odin24]

Why would a production company not utilize all of a BD's capacity, whether it's BD25 or BD50? I'm not talking about leaving less than a couple of GB, I mean leaving approx 9GB on the table.

The Strangers disc size, at least accordng to my PC, has a whopping size of 16.4GB of content, including both versions of the movie. I know seamless branching would allow for the saving of disc space by cutting to the director's cut scenes from the theatrical version, then back again, but what's the point?

This is a BD Live disc, does that consume any of the disc that the PC would not see? At least throw in a few more features or audio track options (DTSHD and PCM), wouldn't this be better than leaving wasted space?

Could someone please help shed some light on this for me?

Thanks,