Not only API, mostly backend. Walking graphs is inherently more expensive, to avoid cycles, than walking tables. Graphs are only for lazy people which cannot remove their up and side links from their data.
It's called normalization for a reason
When I was looking into it the "GraphQL" name was kinda misleading. It's not particularly graph-oriented, and not even especially good at representing graphs in general. Tree-oriented, a bit, I guess, which is a kind of graph. Maybe that's what they're going for.
No idea if this is true, but I think that it's because GraphQL is kind of the successor to FQL, which was used to query Facebook's "social graph," which was a big marketing thing back in those days.
