The sad truth is more than 85% of forest fires are started by humans–whether it be mistakenly leaving a campfire untended, tossing out a cigarette butt, or intentional acts of arson.
Lightning strikes cause very few wildfires. Lightning is 5x hotter than the surface of the sun. But if it strikes the ground, it is more like to fuse dirt and clays into silica’s due to the extreme heat instead of creating a fire. The same goes for a tree if it is struck by lightning. The tree will likely sustain damage from the strike but no fire will break out. It’s not that often that conditions are dry enough and the surrounding materials flammable enough to start a fire. It does happen, but people are responsible far more often than lightning.