GraphQL forms a strongly and deliberately typed interface between a client and server, without frontend and backend teams having to collaborate on the shape of the endpoints (should such and such endpoint gain new options? should it be split into a separate endpoint? should the old one be deprecated, and if so, do clients still rely on it?).

Instead, they need only agree on the shape of the data available, and the frontend queries it however it needs to be queried while the backend resolves the nested calls with no additional effort* from those writing the backend.

Also, some clients come with additional affordances for hard problems, like pagination.

* okay, fine, you have to wrap your data resolution in Dataloaders, but that's not particularly challenging