I have a similar issue with headphone cables failing, often far too soon, but I get that too. It's wear and tear from being yanked and moved. They're also often cheap headphones. But I've had apple cables disintigrate when stored in a cupboard and not moved at all. It's like they're biodegradeable.

I suspect they're using a softner which degrades the plastic over time. Their cables are softer/more bendy than cheaper/stiffer plastic cables.

But for the price they charge, I don't see why they couldn't make them fabric covered. You can buy fabric covered cables for really cheap online, and they ship them half away across the world and still make a profit. Why can't apple do the same?