All you said is true - but these investigations are often used for the purpose of determining financial liability and often that comes down to figuring out that one, immediate, proximate thing that caused the accident.
A whole bunch of things might have gone wrong, but if only you hadn't done/not-done that one thing, we'd all be fine. So it's all your fault!
A whole bunch of things might have gone wrong, but if only you hadn't done/not-done that one thing, we'd all be fine. So it's all your fault!