Hair from a live body doesn't have decomp on the roots, because the body it came from is alive and not decomposing.
Hair from a dead body has decomp on the roots, because the body it came from is dead/decomposing.
I read up on this a couple weeks ago, and I put it in very simple terms because I'm just a plain ordinary person. It's all scientific, but that's what it comes down to. That's the bottom line.
I believe Michael Baden explained that after death there is some type of "band" that actually forms on the hair itself. This band ONLY forms after death.