The problem with templating YAML is that you're templating text, in a very sensitive to whitespace syntax. By definition, Jsonnet avoids that because it operates on the data structure, not on their stringified representation.
My experience with jsonnet varied: there's good jsonnet code, and there's bad one, too. Just like with any programming language, you have to apply good software engineering practices. Text templated YAML, however, is terrible by design.