Ask HN: Why GraphQL APIs but no Datalog APIs?

Why doesn't anyone use Datalog (or another limited-by-design logic programming language) as the query language in a public Web API? The adoption of GraphQL suggests demand for letting the API user write more sophisticated queries even at a performance cost per query. Datalog would let the user do more, likely saving many HTTP round-trips. A lot more research exists on optimizing Datalog than GraphQL. It is unclear that the total impact on performance would be significantly negative compared to the typical GraphQL API. If this line of thinking is valid, where are the Datalog API experiments?