Because a stranger has an outside view. A stranger can see when something is weird or broken, and shouts when that weirdness or brokenness hurts them, versus th

Because a stranger has an outside view. A stranger can see when something is weird or broken, and shouts when that weirdness or brokenness hurts them, versus the insider who is numbed by familiarity into taking the behavior of the system for granted. It's not just software, either! There's a common social phenomenon known as the "broken-stair" problem, where you have a toxic, abusive person in a community, and everyone in the community has just gotten used to that person's behavior and normalized it. Sometimes it takes an outsider to notice that this toxic person is a net harm to the community.