They become, in effect, Spokespersons for the corporation whose wares they are hawking. They become identified with the product. If you are tied to Pepsi you will not be asked to do Coca Cola or any other soft drink. That s called exclusivity. Intellectual property rights have a long history.
Performance rights have a long history, too.
We accept the principle that the person who invents a new widget has an on-going right to be fairly compensated for their work product. That s what patents and copyrights are all about. Licensing Agreements are a fact of life. The other name for residuals is royalties, a familiar term in the world of music where producers, writers and performers are paid a set percentage based on sales. Interestingly, performers are not paid for air play as are writers and producers, but that s another essay.