Dhall is also a JSON generator. And you could write your own Dhall implementation that lets you consume it directly from an application if you want to, it's just nobody's considered that worth doing.
Which is odd because tons of applications in the wild already have this amazing capability of directly consuming python and Haskell without first converting to yaml. But of cause you still have the ability to both produce and consume yaml if that’s needed for some reason.
What applications directly consume Haskell code? The only examples I can think of off the top of my head are apps written in Haskell that actually get recompiled any time you change the "configuration" Haskell code.
As for Python, that's because the Python interpreter can be embedded in an app.