You do not get severance if you quit. Nobody is automatically entitled to any severance legally, ever, unless you were hired under a contract such as a 1099 employee and you have severance written into your agreement. Standard W-2 employees usually do not get severance.
Neither the California Labor Code nor the federal Fair Labor Standards Act require employers to offer severance agreements to departing employees. Instead, severance agreements are provided by employers to accomplish a specific goal.