Maybe "failed" is a strong word.
I just don't see Ada used a lot anymore. This isn't a value judgement on it being "good" or "bad", lots of bad languages (like PHP) end up getting very popular, and lots of cool languages (like Idris) kind of languish in obscurity. Don't mistake me saying popularity is proper metric for how "good" something is.
When I say "anachronistic", I don't mean it as a bad thing either, just that it's not used a lot anymore. I've literally never heard of anyone writing an Ada application in the last twenty years outside blogs on HN.