The direct buried primary line would be unusable to the power thieves, unless they had their own transformer, and the knowledge and tools to tap into the primary feed...Highly Unlikely!
thats how they do it for gas lines. ie Regulator at the meter Rarely do you see alot of gas theft.
Ammonia is a diffrent animal because of meth, you'll get idiots doing homemade hot-taps on high pressure ammonia pipelines and installing bleeders so they can steal pure ammonia