So they came up with something that implemented the Relational Model in a simple way, one that would attract new converts. SQL has plenty of warts and defects, but its success at extinguishing every other database query language can't be denied.
The relational model with unions of conjunctive queries at its core is excellent. SQL on the other hand feels like some weird COBOL dialect that gives you an incredibly verbose implementation of it.
With that said, there are a few enterprisey NoSQL databases which are relational yet provide a nicer language to work with than SQL. I mentioned datomic (which also has persistence as its key feature), but there's also TypeDB which lets you use the first class support for recursive queries to support inheritance more easily. And of course there's google's Logica language which compiles to SQL and lets you use datalog syntax and the ability to write reusable queries, though it doesn't support recursion due to the nature of its target.
Sadly a lot of the "NoSQL" hype later on was led by people who had no clue about database theory, and proceeded to throw the baby out with the bathwater and build whatever abomination MongoDB is, rather than taking SQL's theoretical basis and building a language on top of it that is actually designed for complex usecases. There were only a few exceptions like say Datomic in Clojure world that did NoSQL right.