The entire JSON specification is shorter than just the table of contents of the YAML specification!
Another thing I like about JSON is that you can format it however you want with the whitespace. Want everything on one line? Just write everything on one line!
If data can be represented as a JSON, then there’s generally only one way to represent it in JSON (apart from whitespace). In YAML the same data can be represented in 1000s of different ways. You pick one.
This is the major reason for me. I really liked yaml, because it is way more readable to me than JSON. But then I kept finding new and more confusing yaml features and have realized how over-engineered it is.
Yaml would be great language if it had its features prunned heavy.