Fire suppression plays a role because it
allows fuel to build up to unnatural levels: “The effect of fire suppression has changed over time. Throughout the twentieth century the impact was to exclude fire. However, as more and more natural fire cycles were missed, forests have increased in tree density, and many of the saplings have remained suppressed in the understory. This has the unwanted effect of producing ladder fuels capable of carrying surface fires into the canopies of the dominant trees and converting surface fire regimes into crown fire regimes.”
This is especially the case in forested regions (e.g. Northern California, Oregon, Washington, and British Columbia.) SoCal chaparral is different for various reasons. Fire suppression has probably helped there.