If neither the mods nor users feel heard, who does this “platform” serve?
I see a lot of complaints, about questions closed as redundant etc, and about moderation, but what keeps someone from putting a better version up? In particular unlike quora, the reputation of the person answering doesn't seem as important. most people would accept anyone's answer as long as it works.
so what's the important network effect here?
The (unilateral) relicensing was another recent issue, but generally not. All user contributions are licensed CC-BY-SA 3.0 so I don't see legal reasons stopping you. Google won't send you any traffic, though, because it will be duplicate content and the original has a gajillion links pointing to it.
# see https://stackoverflow/something to understand the next two lines
And then one day SO closes.
(I saw some software build pipes explicitly looking for SO comments and rejecting the code)
That's the first-order effect. The second-order effect is that people who are familiar with one of the StackExchange sites, if they have a question about something that doesn't fit there, might default to looking at the sibling list of sites to find a good place to ask their question, even if that sibling site is smaller than some out-of-network Q&A forum on the same topic. The smaller sites in the network don't quite gain cachet from being associated with their larger siblings, but they sort of gain "an expectation of having your question answered" inherited from their bigger siblings—whether it's true or not.
SE is dying. The quality of the questions is falling because being welcoming to new users is deemed more important now than the newcomers absorbing the culture. Questions go unanswered. The real technical Q&A is on Github now. But this is what Spolsky and Atwood wanted all along, good luck to them with their new community of newbies and SJWs.
When I Google a question, an SE link is still the most common thing
Yep because SE gained critical mass, and in its earlier incarnation was often linked to from outside. But in its present form recent question are unanswered and old answers are obsolete. Because all the people who actually did the work were told by SE that they had served their purpose and were no longer welcome.
It does raise the question of what happens when StackExchange shuts down. There's a lot of knowledge stored there, hopefully it's not lost.