There is not enough dry brush and debris that would sustain a wildfire within urban environments. Roads and concrete are pretty much firebreaks. All these places you see burning like this town, Paradise CA last year, etc, are places that are absolutely surrounded by kindling that has accumulated over the course of decades and was never cleared out or allowed to burn in a controlled manner. Plus, once you get close to the population centers you pretty much have a local airforce putting out fires and hundreds of firefighters.