I'm fairly certain people like me are confused by Prolog not because it's declarative but because it's a logic programming language. Which is more exotic than a functional one with even more esoteric syntax.
I have a feeling XSLT would be better known (i.e. be able to justify investment into learning) if not for json/yaml popularity. Though XML is not particularly human readable anyway. The next logical step after https://json-schema.org/ would be JSLT I imagine.
On a related note, Maven is a great example of a declarative build system. Both Gradle and SBT were gigantic steps back.
But on the flip side, Excel spreadsheets are declarative, and they're the most commonly used programming language in the world. Declarative programs can be simpler, when simplicity is the goal.
Whoever came up with that ... XSLT or Prolog are declarative yet I challenge both of them to be hard to understand