Huge forests with little to no management in vast wilderness areas. Many villages towns and even cities are located within heavily wooded surroundings. Decades of infestations of insects prior to fires that were so big they were also impossible to manage. Decades of preventing and suppressing fires completely with the knowledge that they were vital to the ecosystem. Intense sudden heat waves. Almost complete lack of snow and rain in winter/spring. More severe summer weather mainly thunderstorms.

Lots of reasons really.