What is the primary reason California has so many wildfire ?

Dry climate.

Explanation:

There's more then just one reason, but the main factor is the dry climate. Other factors include arson, careless residents, ect. ect.

California has so many wildfires because it gets most of its moisture from the fall and winter months and likewise, the vegetation spends most of the spring and summer seasons drying out, which essentially leads to fueling and spreading of fires.