'Only scanning for the things one is working on' to the point of missing huge security holes or safety risks is exactly that's wrong with the industrial division-of-labor approach. Workers start to assume that even if they do notice a problem, someone else is either going to fix it or has examined and OKed the current procedure. Workers who speak up and assert that something they noticed actually looks more important than whatever task they were originally assigned to are typically punished rather than rewarded, and fired if they make too much of a fuss because otherwise managerial authority might be diminished. Most firms run internally like a dictatorship, and given Facebook's absurd ownership structure (where there are voting and non-voting shares Zuckerberg retains a majority of the voting shares) it's a recipe for dysfunction.