Dave, I agree with you that GRE is not very suitable for many buried cross country pipeline applications , but would classify what you describe as repairs, of which there can be many and not maintenance but we're probably splitting hairs here. GRE is also quite susceptible to abrasion damage and give its high poissons ratio can move significantly at bends by pressure forces alone. If you have a stone there then it can wear through over time.
The issue is often one of ignorance of how to handle and lay this material compared to steel or flexibles.
It has its uses, but finding enough people experienced in its handling and construction can be a challenge.
Several hundred miles is some network of GRE though, where was that and what did it transport?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.