Many of these houses are decades old and were built in areas that weren't fire risks when the houses were built; Altadena had the opposite problem: it generally

Many of these houses are decades old and were built in areas that weren't fire risks when the houses were built; Altadena had the opposite problem: it generally received a lot of rain so people were concerned about flooding and mudslides and so a lot of the infrastructure is designed to maximize the channeled flow of water down the hillsides. Also, a lot of the houses burning in the Eaton fire (especially in Altadena) are surrounded by miles of development, but very-low-humidity hurricane-strength Santa Ana wind gusts can carry (and keep alive) burning embers for miles.