You are asking for a rational explanation for why something better is less popular than something that is worse. The answer almost certainly is "just because",

You are asking for a rational explanation for why something better is less popular than something that is worse. The answer almost certainly is "just because", and more specifically "because Facebook made GraphQL, not Datalog". Graphql had a lot of hype around it when it was first announced. It so happens that I had just learned Prolog at the time and was personally bemoaning why SQL was so popular when a Prolog-like solution would be so much better. A month or so later comes all the podcasts and articles on HN from Facebook devs about GraphQL. Datalog is a really great technology, and the idea that you can guarantee that each statement terminates is very powerful. GraphQL seems to be a great technology when you have an extremely specific requirements. I personally would certainly use it if i had those requirements, but IMO it seems totally unjustified for your average tech company.