The limitations of the query language make code size explode the moment you step outside simple toy examples. It doesn't have any concept of a JOIN, or of the actual relationships between your types (graphql has no concept that me == me.parent.child). You end up writing data loaders for every type so that loops in your schema can be resolved efficiently.
Managing permissions is so much more of a pain compared to REST because exactly what data is returned is so much more dynamic. If you have some confidential data nested 10 layers deep in the query, you get two choices. Either fail the entire query with a NotAllowed based on one deeply nested field that the client maybe does not even care about, or you have to make your schema super loose and make every single field that's subject to permission management nullable. So much easier on a REST endpoint because the response is more constrained.