It's a slippery slope. What about consultant developers that worked on the codebase of photoshop 10 years ago, whose code is still used in the current version? Do they deserve a percentage of the subscription? And architect who designed it?
This is the reason studios can do this, because the contract was very exceptional, and they want to make it similar to any other industry, where freelances and employees do not share any long term revenue
Do you have examples? It should only happen in case of overfitting, i.e. too many identical image for the same subject