Because its a waste product, but once we make digging up fossil fuels illegal, that will change. Then we can repurposed the infrastructure in ways that are not harmful
Its a battery. It makes more sense than electricity because its extremely energy dense, can be transported long distances far more efficiently than electricity, and can be stored indefinitely in low-tech gas tanks instead of electrical batteries
We can make synthetic methane with renewable energy though. I don't have a problem with building such infrastructure becsuse it can be used with renewable energy