See sibling posts for the cost argument.

> These homes would have been destroyed regardless of building material.

That's just not the case. Fire-resistant construction might not always help the first house at the subdivision's edge, but it will help the rest. One analogy is control rods in a reactor.

As I said in another post, the problem with firestorms here in CA is the rate of initial spread. We always get massive numbers of destroyed structures all at once, and <25% containment until the winds subside. The ignition source for most of the structures are burning wood-frame structures. Early on, firefighters can only help evacuate people.