I think performance is not the main reason for going stateless for most people. With stateless you can more easily achieve HA of your auth server. Since it is a

I think performance is not the main reason for going stateless for most people. With stateless you can more easily achieve HA of your auth server. Since it is all stateless your auth servers dont need to know about each other. However with stateful you need somesort of special HA construct between instances of your auth servers otherwise they don't know which sessions exist.