Because it's distributed and the larger the spread, the smaller the obvious scale. For example, let's say I'm a murderer and kill ever resident of a single str

Because it's distributed and the larger the spread, the smaller the obvious scale. For example, let's say I'm a murderer and kill ever resident of a single street, one household a day. That's way too much of a coincidence to ignore. But if I did the same number across a larger area, maybe you get different police forces that haven't thought to talk to each other and no one spots the connection until much later. The same applies here. If you personally have faulty software, it's not great, but you probably move on. If your employer buys the same software for all of its employees, then the scale of the problem is much more obvious and the actual cost of the problem is a lot larger to a single entity.