Psychologically, what is going on the minds of wildfire-arsonists?

It's not just insane and reckless, it's ludicrous. It is malicious and serpentine and a close to evil as I've ever heard of. It's up there with torture, bu a least that has a single victim. I'm literally asking, What kind of deranged lunatic does someone have to be, for them to set a wildfire, and menace society at large? Sadistic pyromania barely seems to scratch the surface.