Again… this is your mistake. You have it 100% backwards.
The light is not associated with the object. The subgraph is associated with a light.
It is not saying “Attach this light to the object”
It is saying “light this portion of the graph with this light.”
You can associate that light all over the scene graph. Which one should move it?
The fact that other engines don’t support this concept is their limitation and not ours.