They started dying when they did away with their catalog. If they’d switched over to Internet at the time they would be ruling the world instead of Amazon.
The last catalog was in '93 - when the Internet was still a new, mostly text and crude graphics experience with dial-up ISPs. The broadband that they needed for catalog-like images was still years away. I've always thought the screw-up was in failing to continue the printed catalog as a computer-desk reference and supplement to online ordering (using a stripped-down online catalog/ordering desk/whatever). The parts were all there, they just didn't put them together.