Google+ comes to mind and the time when thousands of engineers couldn't stir the interest of public to turn to the service
AR is a little different because it's not a product; Facebook's AR apps might fail, but Zuck's vision could still succeed if Facebook create (or acquire) tools for creating an AR ecosystem.
all they really need is a collection of millions of AR-related patents allowing to sue any entity doing anything AR-related
Google search was minimalist. Android followed everyone else in the market, and hasn't iterated core UX much since. G Suite office apps were acquired, and mostly cloned Office online. Same with Gmail.
Maps is about the only heavily-used app, and I wouldn't call its design revolutionary (or even good).
Chrome is about the best example I can come up with, and it's mostly iterated and improved on the back end.
Maybe I'm missing something major? But it's not a market they compete in or are particularly good at.
(This isn't to say that the initial lift of desktop apps to the web wasn't a technical tour du force; just that blue sky GUIs have never been something they're known for)
That's a feature.
> Maybe I'm missing something major
Yes.
Two of the largest online social networks to date have emerged from the highly-selective university space: Usenet (UCLA, Stanford, Berkeley, MIT, UI, Rutgers, etc.), and Facebook (once: literally Harvard).
Google+ might have been able to grow from its tech roots. My sense is that Google's marketing-and-advertising focus (and community), as well as gross mismanagement, doomed its attempt, nudged with some active antipropaganda from other sources, notably Facebook. That's not to say it would have succeeded, but there were numerous self- and externally-imposed injuries.