AFAIK, libfyaml[0] (not to be confused with libyaml) passes the 1.2 test suite, and if I remember correctly, it's currently the only YAML loader with that claim at the moment.
The yaml.orf website also lists a bunch of implementations, with about 1/3 supporting 1.2. I'm guessing that the users of those libraries just happily hum along and we never hear from them!
The issue is that downstream consumers of popular languages with a vocal community here on HN tend to just pull in libyaml, PyYAML being the major offender in my mind.
[0]:https://github.com/pantoniou/libfyaml