They do say that old blades are the most coveted, as are old hilts made of rhino horn I imagine the focus on the scabbard is partly because it was largely deco

They do say that old blades are the most coveted, as are old hilts made of rhino horn I imagine the focus on the scabbard is partly because it was largely decorative and served a very different function - such as being collateral. So all parts of the blade were important, but the part "used" the most has highest investment. If you don't draw the knife, then it gets most use by having obvious skill in its crafting.