Have you considered that Quora is failing because it's user-hostile? I do not visit Quora links on Google because I know it's going to tease me with a snippet and force me to login.
I just don't click Quora links anymore.
OTOH a lot of legitimate questions were answered by specialists or people very familiar with the subjects
Generally, I find Quora to be a pretty "ok" place to have a conversation. Better than most of Reddit, for sure. (Reddit does have some fantabulous subs to be sure, but not very many! :-) )
EDIT: HN is good for conversations in threads, although they can veer off track pretty wildly. Reddit can get pretty vitriolic. You could have a conversation, but the participants destroy it. Twitter? Fuggedaboutit. Are there sites I ought to look at where I can have a polite discussion with people that I may or may not agree with on various topics? [FWIW - Before 2008, Reddit itself was pretty close to this, except for maybe /r/politics]
I only go there to read a few people's opinions on things. If you restrict yourself to those people then Quora seems ok. If a Quora link shows up in my search results -- I know it's going to be useless.
The only problem is Quora seems to aggressively promote clickbait scammers / self-promoting twits. I find myself actively logging on to Quora very rarely these days as it becomes harder and harder to repel useless content from my feed.
To me Quora is just a more entitled/self-righteous version of Reddit, and much less fun.
It is Quora itself that needs to justify against that valuation, not anyone else. Where that is fine or not, I think the news itself is self-explanatory.
I'm finding it hard to think of other domains with succesful quasi-public institutions run by for-profits without monetization. Are there other examples?
It works really well for blocking quora from google results.
Before that, Quora felt like a small community similar to HN. They had founders and executives answering questions. They were still spamming email afair but not as aggressively as today and it didn't have what is x + 3 = 10?
I deleted it after I reached a million answer views from a sudden growth. The users that moved in completely destroyed the whole thing.
That day, I learnt acquiring users via heavy marketing or SEO may not be a good decision for a community. They are better as spectators or consumers.