The reason to why many of the file formats seen in KOTOR bifs are not possible to mod yet are because they are new, or enhanced versions of already existing formats found in NWN among others.
Of course they have to be, just look at KOTOR - does it look anything like NWN to you?
Either way, we are just beginning to unwrap KOTOR and finding out what we can do with it, I doubt Bioware made any deliberate changes to make it more difficult for us to mod(that just isn't how a corporate game developer works) although it might seem so at times when you can't get your latest mod to function or that script to run etc
Difficult to mod? at least we have some foundation of tools we can build upon, many games come completely unsupported and unknown from start with no previous titles of a similar engine which you can use as reference, in fact i'd say we are lucky being able to use some of the NWN tools to make our mods.
When I first sat down and decided to make a working script modification to the game, it took me several aggrivating days until I got it figured out and working(at one time I stopped trying because I figured it was impossible, too different), you wouldn't believe what I try in between before I puzzled out how to do this and that..lucky thing it was so easy in reality thanks to Aurora Toolset and I think it is the same way with many other things in the game and with time we will figure them all out.
PS. Pardon my long, ranty post now