I think it might be that they were so successful at convincing a large percentage of their cable customers that they needed expensive cabling, why bother carrying the cheap stuff at all? Combine that with the fact that people don't want to wander all over town just to find a cable, and you've got yourself a guaranteed-sale 100% markup item.

Even Radio Shack barely carries cheapo cables any more, and they're the kings of cheapo electronics.