My most favoured scenario is one where the house is sad and dilapidated and just wants to die. So much so, that it becomes sentient and psychic. Somewhat psychic as it could only communicate within a very specific metaphysical orientation. The arsonist was the only individual in the world who was compatible with the house's transmission. This connection does not respect physical distance, so the arsonist, being many miles away, responded to the call. He studied the house and found the perfect timing to grant its wish.