Actually, a good many destructive fires, especially in Southern California, result from deliberate arson, like our recent biggie near Los Angeles,the Station Fire.

They are often destructive because the kooks who set them choose optimum conditions for ignition, most particularly Santa Ana winds.

I believe about half of all wildfires, in the US at least, result from lightning strikes. Many of these can be insignificant, because they may be accompanied by rain.