Today, the priority is to avoid the spread of smoke and facilitate evacuation. Once everyone is out, it doesn't matter much if everything burns down, as in a fierce fire everything would likely need to be demolished anyway.
The reason buildings are not made of stone is that it is extremely expensive, mainly due to the amount of labor hours, it's poorly insulated or requires extremely thick walls, and it's heavy (the total weight of the building).
In the past, technology was expensive and labor was cheap, today it's the opposite.