GraphQL is great for exposing a single API that hides the complexity of the systems behind. As such, it is commonly use to aggregate data from different data sources. For example, databases, services, etc.
But most corporate web services are build around RESTful APIs, hence it is crucial to handle this use case efficiently.
Given the reference implementation for GraphQL is written in node and the close relationship between the frontend and the language, it is very popular to use node as the platform for the server.