Now, please explain to me why I can take a piece of wire installed in a
house in 1968, more than three decades ago, and bend it back and forth
until the copper inside the insulation work-hardens and breaks, without
any cracks or any other kind of indication of failure appearing in the
insulation, if such insulation will "crumble" in "decades".
Compare that insulation with new cable and see if it's as flexible.