Look willpell, we're not mind readers. We're not the game designers. The game designers do not (as far as I know) come to this forum to answer our questions. They had their own forum for that, but it's devoted to newer editions of D&D now. We don't know why the game designers chose to write something the way they did unless they came out someplace and told us, which would be a heck of a thing to track down now if it even ever existed.
All we can do here is to examine and interpret what the books tell us. "Why" is a question best left to philosophers.