YAML permits comments. And it is easier to read than JSON. I can look at YAML source and see: "Oh, that's a blockquote, and that's a table of key-value pairs."
But I have NEVER been able to write either of those syntaxes from memory; I always need to reference another sample of YAML code, or look up the docs. Maybe if I'd done more k8s stuff I'd have yml beaten in my head?
And that was all BEFORE they decided to make YAML a superset of JSON...