Social networks, like space launches, are complex systems, with many failure paths and few leading to success.
Unlike sppace launches, there can also only be a single leading platform in a winner-take-all regime, making success far less likely than in rocket engineering.
G+ failed for multiple reasons, despite being successful in numerous particulars. I miss it, though I don't regret its passing.
As with other criticisms, this one is on point in noting that the failures were of leadership (and all the way up the stack: Bradley, Vic, Larry, Eric), and architectural.
Site mechanics (good points by Talin), unreliable messaging, and the "let's cram this down everyone's throats" elements all left a very bitter taste.
What Talin omits in particular (though it's alluded to briefly) was the extent to which Google directly fought many of Google+'s biggest enthusiasts, with #nymwars (the Real Names policy), noted, being only one of the most notable instances.
I'll also distinguish G+ fans from Google fanbois -- the latter were (and remain) toxic to the company. Thos includes many (though not all) of Google's annointed "TCs" (top contributors), many represented among the G+ Google+ Help community, where active frustration of efforts to help users and groups migrate off G+ in its final months and days was a constant factor.
Another element creating tremendous distrust was Google's repeated ridiculous statements as to the site's success, openly mocked in the press. In early 2015 I proved by a random sampling of profiles that a minuscule fraction of the billions of registered profiles were posting publicly on a monthly basis, methods and results confirmed several months later, on a far larger sample, by Stone Temple Consulting:
https://www.stonetemple.com/real-numbers-for-the-activity-on...
Later 2018/2019 analysis of G+ Communities further cemented these findings. This also showed the huge value of regularly contributed, fresh, relevant content to success, over raw subscriber counts. Post recency was a far bigger prediction of other engagement (comments, +1s, reshares) than subscribers.
See:
https://social.antefriguserat.de/index.php/Migrating_Google%...
That Google, a notoriously metrics-driven firm, could not or would not credibly analyze or report such data was a huge blow to its general credibility.