It's one of the most hilariously insane plant life histories ever. Most plants that exhibit serotiny (cones or seed pods that only open in response to smoke or flame) drop their seeds and wait for a small brushfire to come along and clear out the undergrowth. Blue gums overdo it by keeping their pods in the canopy and actively accelerating any fires that happen so that they're the only thing left to grow in the ashes.

And of course people took one look at wildfire prone California and thought to themselves "Oh man, we need to plant a ton of these trees here"