Used to be very common, then the market for scrap copper sort of dropped out and a lot of the theft stopped. Site owners also go smart and started coating the copper ground busses with tin and made them look less valuable. Some even use wire that's marked with the owner and "do not accept for recycling".
I guess some people are really hard up for cash. The risks from doing some of that are high. No shortage of stupid people that electrocuted themselves trying to steal wire. We had a site where someone stole the wiring. No idea how they did it without killing themselves. Big scorch marks where they got their cutters between the wire and the panel. Funny thing was that our co-gen plant operators saw a 'disturbance' on the utility power feed at the time it happened. Didn't put 2 and 2 together until the next morning.
If it's Heliax they stole, then they'll have a hard time recycling it. Most recycle centers don't want the foam dielectric.