[Video] 2D hinge joints not working.

I've got a situation where I'm attaching 2D hinge joints to a "stem" object, to try to make a chain/rope thing, as in the tutorial for 2D hinge joints by Unity. However, when I press play, it doesn't fall or work properly -- even though none of the 2D joints have kinematic rigidbody 2d's. They just float there in space, not reacting to gravity.

When I use the mouse to translate one of the sections of the rope in the scene view, that one section of rope starts to move and swing with gravity, but none of the other ones move. Is there a reason why this would be happening? I feel like I'm taking crazy pills here!

Here is a video of it happening.

https://www.youtube.com/watch?v=ePuduprsZ74