Re: Do the work, get paid, move on
They don't have to do it that way. They could easily pay actors the same way they pay many other people who do jobs, creative or not. Mine, for instance. I get paid to write some software. They don't pay me each time they run it. We negotiated how much they had to pay to get the software when I was hired. If they do that with an actor, no problem. The reason they don't is usually that they don't have enough money to do that, so they offer to continue paying the actor from money that comes in later instead of paying up front. You could also do software that way: I'll get paid less while writing it, then you give me a portion of the license fees.
Neither has any connection to the AI work. If they buy the software writing from me, they get that piece of software. They don't get other pieces of software I write. They don't even get fixes to that one unless I am still employed. When hiring an actor, you don't get rights to everything about them forever, you get the rights to the performance they just did for you. You want to keep showing that video of them following the script? Great. You want to use their picture in a big machine learning training thing? Get permission to do that or you don't get to.