I have talked with friends of mine who are Firemen about this. They say it's because environmentalists have successfully lobbied against Controlled Burning.
From the Gayley Fire:
Climate experts are apparently backing President Donald Trump’s repeated arguments that California’s wildfires were a result of poor land management rather than climate change, E&E reported Thursday.
Roughly 75% of damage stemming from California’s wildfires was a result of “the way we manage lands and develop our landscape,” Scott Stephens, a professor of fire science at the University of California, Berkeley, said Wednesday at a conference in Washington.
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