You have YAML/JSON that k8s API wants, that is fed through helm which is fed through helmsman or whatever newer thing. There might be a layer or two of other templating around. Sometimes companies have built systems so developers/devops don't even have the ability to see what the final compiled version of the template is which is like the mother of all: "works on my laptop" problems.

It's super easy to break text based templating because of some space, tab, string escaping or whatever.

YAML makes it worse as there are lots of gotchas and different ways of doing. JSON, being quite verbose and inflexible at least has strong structure right in your face so it's a bit easier to figure out what went wrong.

With a proper programming language data structure you can be much better with verifying that the things you add or remove or iterate over will produce a valid result, much better refactoring and working as a team independently.