The main two reasons employers offer severance are –
(a) A gesture of good will – employers offer severance because they have an interest in preserving a good will in the industry and make the transition of a separated employee to another job easier, and discourage the employee from saying about things about the company by making that employee a confidentiality and non-disparagement agreement. Of course, severance payment is not guaranteed to achieve this goal, but softening the overall impact of termination is a good business practice.
(b) Avoiding litigation headache – whether you have a case or not, you can still make allegations and fight your employer in court or DLSE, etc… Even if there is no evidence of violations, it will take time and money for your employer to dismiss your case. An employer has an interest in making sure that they don’t have this headache, and they may be willing to pay a certain amount to have you sign a release and waiver and have the peace of mind that you will never come back and sue them for anything.