When europeans arrived, the state had regular fall wildfires (smoke was constant during this time) from natives setting regular fires to burn out undesirable plants and keep things useful for them. In Yosemite for instance, this allowed the land to support them with acorns from the black oaks there. Trees were monstrously huge compared to areas now, and relatively sparse and manageable. No known mega fires, although it probably still happened from time to time.
Now in most areas, it’s tangled brush and super dense and diseased trees (or just tangled brush where it is too dry for trees), with large scale mega fires and tree mortality due to disease.
Cutting down the old growth didn’t help of course - but even in places where trees have regained nearly the same sizes or were kept intact, the brush growth is a big problem. It’s natural for regrown forests to be dense, and the weaker trees die as they get crowded out. It isn’t normal for nearly every forest to be doing this all at the same time in a region due to suppression of the fires that normally clean out the junk and/or reset the clock in small areas.
Big Basin state park for instance was not logged, and it burned to the ground during the CZU complex fires due to all the built up fuel. If burned every year, it would have died out before being able to do much if any damage.