I think framing people "staying put" in a solely negative light paints an incomplete picture. I'd bet that the biggest reason people stay put is not anti-social but pro-social--tight community, cultural, and family bonds.
Who knows? If not for those policies, Pasadena could have been built denser and Altadena could have been miles of flat natural reserve that acts as a large firebreak where firefighters can easily fight the flames before they threaten thousands of structures, with frequent prescribed burns to keep the fuel load down.
That's probably the real kind of conversation we should be having of municipalities easing housing restrictions to build denser and the state buying up large swathes of these wildland adjacent communities to create larger breaks between the hills and the houses.
Perhaps we should build different though to mitigate risk. It's not hard to build a fire-proof house. Or one that's flood resistant. Or hurricane proof...