Fixing Facebook isn't a hard problem. Fixing it while keeping advertisers happy is pretty much impossible. If you try to be more vigilant on privacy settings then you give advertisers less choices to target people. And with Amazon moving into the ad market aggressively, and Google being the behemoth that they are the last thing you want is to hurt your advertising platform.
You can take a look at the entire ecosystem of React code out across so many repos and documentation sites, and then stand that next to Facebook proper, and then note the difference in tone, quality and psychological warfare.
With that in mind, consider what kind of strategy and tactics Facebook's internal operations must be operating.