Except that there is implicit dependency management.
It would be like saying that all SKUs need to be comprised of other SKUs and less than 2kg of screws, nuts, bolts and custom components.
In your analogy the Spring might be an entire engine, spark plugs and all, built as a single unit. Want to use your own spark plugs? Tough luck. You get the whole engine or none at all, or you could just build your own from scratch.
LOL, I'm trying to imagine anything else in life being run like this. For instance, you go to the "car package manager" and are told that all parts must be less than 2kg and that you need to choose which ones you need...