Well, maybe they think that it's worth "hating" on it because people are using it, and they want to make people aware of the problems? I know I do, though "hating" sounds like I have malicious intent, which I do not. I am sure the creator(s) are very bright people with nothing but good intentions. But I agree with the article that YAML is frustrating to work with. The "it's not perfect, but neither is anything" argument is a bit of a cop-out in my opinion, as that can be applied to anything and everything.
I feel (but don't know!) that YAML was inspired by markdown as an attempt to create a format that felt like the most natural and intuitive to read for humans, while still machine-consumable. A noble idea, but in my opinion, one that fails as soon as you have more than half a page of configuration. Then, it just becomes a pain to even figure out which parent a specific bullet belongs to. And that's not even getting into all the cleverness.
I don't want to create a new language because [XKCD standards comic]. I'd prefer people use JSON or TOML as I consider those better even if they have plenty of issues on their own.