Because at the end of the drought, a period of rain starts, allowing the growth of many plants that will dry out over time, serving as material to feed the fire of a fire.
As in most of the USA, much of California's rain falls in the fall and winter, at the end of the dry season. In this period the vegetation has enough water to grow in abundance and develop, however in the coming seasons, without the presence of rain, these plants start to dry and dry plants catch fire easily.
The conclusion we can draw from this is that california has many natural hazards because the nature of the conditions for them to happen, allowing plants to grow at the end of the dry period.