The bigger the town the easier it gets. Towns have roads and parking lots and cmu commercial buildings that are mostly non-flammable. They also have water supplies and logistics infrastructure. Centralized defense is very feasible. Mountain roads and poor communications cause an underutilization of resources.
It's simply not possible to make a practical house that won't support combustion. However, we don't need to. The threat is not what happens when the house is exposed to direct fire, but what happens when the house is exposed to ignition sources. And those *can* be stopped. Build your house such that there isn't anything combustible on the outside of the house and all access points are made spark proof.
Our house is not fire engineered--but still it has very few spots that could ignite. That's simply because we have stucco walls and a concrete tile roof. There is some exposed wood but not much. Nor are the vents spark proof.
Unfortunately, concrete tile roofs aren't suitable in many places (they don't like hail) and can't be retrofit onto most houses due to the weight.
That doesn't seem accurate. Commercial buildings aren't necessarily in the outskirts of town. And while the buildings themselves might be slightly more fire-resistant than typical wood frame houses, they're full of flammable materials. Look what happened with the Camp Fire in 2018.