The following video mentions that there are 13 "holy numbers" you need to make the strandbeest walk smoothley. They call them the strandbeest's DNA. The inventor came up with these numbers after a few months of experimenting. After 30 years, he's already working on a brain consisting of 20+ brain cells to prevent the strandbeest walking into the water.
Now, imagine what an ISBE can "invent" when it has millions or billions of years.
As many people already said: The bad ETs are harvesting DNA. It's the main reason why this prison planet is a "profitable enterprise". DNA is the blueprint you need to create bodies that enable the ISBEs to interact with the physical world. DNA is the actual "spice". And they can't produce it on their own.
Now ask: Why can't they produce it, but a dutch inventor can do it with some sticks and zip ties?