Re: A simple (but costly) answer

That makes them much more expensive. They'd have to pay for expensive steel armour (OK, perhaps not expensive in short lengths, but we're talking ridiculously long total lengths here) and the extra weight would also increase the cost of transporting and installing the cable - you need bigger, more powerful equipment for a big roll of thick heavy cable, you can't fit as many in a van or lorry, and installation would take longer.

It's significantly cheaper to just fix the occasional break when it happens.

Besides, normal cable armour may protect against an accidental spade but isn't going to do much against the real accident risk - a JCB (or other digger). And someone who's deliberately trying to steal the cable will get bolt cutters if necessary to cut it.

If you're willing to pay extra for reliability, the right solution is to install two or more cables with diverse paths, so a break only takes out one of them. (Clearly Armenia wasn't prepared to pay for that).