Copper tubing has seen resurgence in its use for fuel gas piping systems. Not that everyone stopped using copper tubing for these systems. After all, one of the most popular piping materials for LP gas systems is copper tubing. My friends in northern Virginia always praise the use of copper tubing in their 2 psi gas systems. They can run smaller tubing since the pressure is much higher.
Copper tubing is also quite popular in natural gas piping systems when connecting outdoor barbecue grills and gas lights. But copper never caught on as a popular piping material for natural gas systems inside a building (with the exception in pockets of areas in the country).