Why are man-caused fires usually worse than lightning fires?

Lightning usually strikes on the tops of ridges and starts a small fire, which spreads slowly, especially if the lightning storm is accompanied by rain. Man-caused fires most frequently start along roads, trails, and streams, in canyons, or on the lower slopes of the hills; they spread rapidly uphill and often become conflagrations. Fires intentionally set, that is, incendiary fires, nearly always occur in periods of high fire hazard.