The reason it is like that is because GraphQL is intended for highly distributed backend where at any time one of those backend services might be unavailable and failing the whole request when only a single deeply nested field is missing would lead to bad user experience.

In short GraphQL is optimized for keeping as much functionality working as possible no matter how much instability there is in the backend.

This is a common problem in REST endpoints that consume data from multiple services as well. But the request usually fails completely. On the other hand REST request don't usually touch as many services as a GraphQL request.