trying to connect a puppet without a body or neck

Because the artwork overlaps and is not marked as independent (the leading "+" character like for the eyes etc), the artwork for the legs is all glued together with the body etc. E.g. the guitar and left and right leg are all part of the one "mesh". So they cannot move independently.

If you just want the legs to stay together but flex at knee joint, you might get away with tagging just one leg (it does not care that the artwork looks like two). You would do things like put a pin on the feet, put a dragger on the torso, delete the sticks for the second leg (keep the sticks etc near the center of the two legs). To make it bob up and down, use the dragger on the torso. The Limb IK behavior should be able to be used to make sure the legs bend the right way, but if you put the sticks on a slight angle (knees forward) like you have already, then you might not need it. It is needed for arms as you may drag the hands all over the place - in your case you would only drag the torso up and down, so it might "just work" without Limb IK. You might need a stick along the bottom of the guitar however to stop it bending.

You can go further and make more things independent, but it also causes problems keeping things aligned (as the layers are "independent" they move more freely, so are harder to line up). So if you just want to bob up and down, I would try to just use sticks to control where to bend and not make things independent.