Unfortunately, it's not that simple. For example, decades of fire suppression created unnatural forests, with more deadfall and closer, smaller trees, that burn more intensely than natural ones. Thanks to global warming, bark beetles have killed vast swathes of forest in the western United States. And people live near those forests, and expect the fire department to protect their houses.

It can't all be fixed and controlled, but "letting nature take its course" would have disastrous consequences at this point.

Then why do we send in firefighters?

I didn't say we should stop the forest fires, I said we want to control them. Almost 100 people died in California last year and there was $3.5 billion in damage:

https://en.wikipedia.org/wiki/2018_California_wildfires

Yes we do try to control them, but that's a last resort, https://www.youtube.com/watch?v=EodxubsO8EI

Same problem with Texas and floods, Florida and hurricanes, &c. building in risk zones is inherently dangerous. The people who died knew the risks.