At $120/mo might as well just get a big propane tank and have a tanker come refill it every six to twelve months. If they’re not using it to heat the house a 500 gallon tank lasts a long time. Bonus points because you can use it as a generator fuel source for the inevitable California power outage and possible earthquake disaster.

They'll ramp up automatically as people switch to the new system and less people use the old system that's sized and priced as if everyone is using it.

In more organized places they are a) ensuring new subdivisions are gas free from the start and b) disconnecting large areas of older connections simultaneously to minimize overheads.