A huge chunk of the state is big, steep, brush and grass covered hills that dry out very badly. All it takes is a spark in some remote valley and you’re going to lose hundreds of acres to a fire and there’s nothing anyone can do, the hills hard hard to traverse and the fire moves faster than you can imagine. Normally once it gets to a more populated area they’re able to fight it more effectively, it’s flatter, you can get trucks and men to the front line, and houses don’t burn quite as fast as grass, but the terrain here is still tricky, and one of the biggest tools California uses, air support, is grounded from the wind. Basically, the fires happen no matter what, but there’s a specific set of circumstances that are making this one pretty nasty right now.
Edit: Controlled burns do help and they happen but you’d have to burn the entire state to the ground every two years to fully stop wildfires, which would be counterproductive.