You know Dominique that's a fair assertion, so I'll give you one here.
Let's say that you do work for a company that is not work for hire, that is that you were contracted and are being paid a risidual or royalty, rather than them owning your work outright.
From there, they sell your work to as many people as they can to make a profit, and then you get a cut based on your royalty or residual payment agreement(s).
This applies to UI/UX if you're designing interfaces or interface frameworks, and would be a prime example of how the money you make would be determined by how much value you deliver at the scale the company delivers it to customers divided by the percentage of your royalty or residual.
Another example may be if you were to design a UI kit and sell it online.
People may buy or license your UI kit, provided it delivers enough value to them for their purposes, and if you have 100% ownership of the product, you make a good deal more.
Do examples like this help to answer your question or are you looking for something more verbose?
Let me know at your leisure.