Why? Is there a good reason for this, or is this just another whim of the murderous deity who you would have us believe constructs such a world with perfect foresight?
Is this really a fair question? This seems akin to Buz asking us something like "why are the fundamental laws of the universe the way they are, and not another way?"
I'm willing to allow blood-redemption as a fundamental axiom of Buz's Christian worldview. It's certainly no more arbitrary than any physical constant, I'd say. Anyway Buz provided the bible quote so that's sufficient evidence to me, within the scope of the Christian worldview.
Challenge his worldview if you like, but I don't see this being a fruitful way to do so... Just my two-hundreths of a dollar.