Heating is easier than cooling. For heat you just run a set of lines from the source to the homes, same as plumbing. To dump that heat into the ground, the field you need grows very quickly. A small town would need a large, and probably deep field of pipes. The cost would be huge. Geothermal is great, but digging is hard, so it's relatively expensive. Every project needs to be individually considered, to determine if it's really the way to go.