GraphQL decouples the frontend team's data needs from the teams managing the API and data layers.

GraphQL was first deployed for Facebook's native mobile applications. Clients and backends had rapidly diverging data needs. Mobile clients were different than web clients. Some APIs didn't even exist (e.g., hydrated serverside and sent as HTML). iOS applications might rarely (or never) be updated.

There's no silver bullet. GraphQL can't solve all problems. But it solves certain ones for certain teams. Whether or not it will become as ubiquitous as REST and RPC, TBD.