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.
That's a choice, not automatic. The government subsides many, many things and that doesn't have to be an exception. They should just continue to advertise the absolute amazingness of the alternatives, train government backed installers, and use the carrot and stick method
Instead of just whacking people with the stick (and leave the installations entirely up to the private sector who have a terrible history of being conmen when it's the government providing grants to the businesses)