The Joinder is a unique feature of California law and it's only required for Local Governmental Plans and Plans that require it as part of their policies and procedures (mostly union plans).
I agree 100% that it's extra red tape that is-frankly-a pain in the rear end with no real purpose. I would jump for joy if they got rid of joinders and took a more reasonable approach-like the other 49 states that don't have joinders.
I feel CA runs a lot of things that way-with no purpose/reason...sigh....but we have great weather and beaches. So here I stay.