A team of researchers said last year that climate change has increased the risk of large wildfires in Canada, where the season usually runs from March to October. Earlier this year, Canadian wildfires also prompted air quality warnings in places including Minnesota and Wisconsin.
Huge forests with little to no management in vast wilderness areas. Many villages towns and even cities are located within heavily wooded surroundings but there are also huge tracts of uninhabited areas. 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.