Where are you seeing this? There are a couple of solutions that follow this model (e.g. Hasura, Postgraphile), but it's not an approach recommended by any of the creators of GraphQL, or the bulk of its users.
Why, for starters right on GraphQL's own slogan? In the fact that GraphQL is sold as the API layer for front-end applications?
"Faster frontend development"?
"Iterate quickly on apps without waiting for new backend endpoints"?
These are direct quotes from GraphQL's front page.
You need to be completely disconnected from the topic to not be aware of GraphQL and it's value proposition.
This is the part I was focusing on, sorry if there was confusion. For context, I've been working with GraphQL since June 2015, so I'm pretty intimate with the topic.
It's worth noting that those slogans you quoted are from graphql.com rather than graphql.org. The latter is the official site, the former (.com) is owned by Apollo and isn't official in any capacity -- something I personally find to be an extremely questionable situation. GraphQL's actual slogan is "A query language for your API".