Because there are many benefits to using GraphQL that aren't supported if you explicitly tie the schema to the data source - one of them being the relative ease of supporting out-of-date clients. Another being the ease of supporting multiple data sources in the same schema, like Elasticsearch, Redis, etc (though I guess you can have PostgreSQL talk to those data sources instead).
My use of "real project" was perhaps a little unfair. What I mean is that as soon as you go beyond the simplest requirements of a GraphQL server, a solution like this is going to present more problems than it solves.
It's just that many people want to be able to use the software by doing modifications to it for their secret sauce. And they don't want to share the sauce. AGPL forces you to share it, even if you don't distribute the software: as long as you make a service with your modified version, you are legally entitled to share the modifications.
Of course, it's almost impossible to prove IRL, but still, a lot of corporations have problems with that. They want the free open source project to make them earn money, no price to pay.
