You're trying to follow broken email threads. Some people haven't replied to all and so there are all kinds of fragmented emails associated with the effort. Then there are the extraneous meeting notes and missives with various attachments. Even if the whole mess is in one of your folders, other people in the effort have their own folder versions. Who knows if anyone has exactly what someone else has. New people to the effort have no way of easily catching up in an orderly way. It doesn't get any worse than this.
This is why email is arguably the best way to prevent efficient collaboration, the kind that would otherwise occur in well-organized, editable shared documents. We should cease all tolerance for excuses featuring impossible learning curves and the classic, that "they barely do email." We need to exercise compassionate persistence. The more people learn how to use shared docs, the more easily they can add their value to the process. The technology is vital to their engagement and therefore not optional.