The prime motivator for it is a certain user experience. I'm not sure they've found the best developer experience for providing that user experience, but I'm also not sure that a better DX is possible - the whole concept has quite a bit of inherent complexity, I'm afraid.
(The conclusion could, of course, also be that it's just not feasible to create that kind of user experience. Luckily, traditional patterns still work just as well.)
If you look at the origins, the primary motivation was finding a way to get a good data loading developer experience without having to adopt Relay and GraphQL.
(The conclusion could, of course, also be that it's just not feasible to create that kind of user experience. Luckily, traditional patterns still work just as well.)