* since members come and go the spreadsheet can become sooner or later almost public again if it isn't that everybody can see only his records
* this means that neither the CM nor the participants cannot be properly checked; and humans are inclined to cheat, you know...
As I mentioned above, I can see the argument for a public spreadsheet in short lived campaigns, those which have a high turn over of users, or those with untrusted managers. But in a stable campaign such as ChipMixer, which adds or removes users only a couple of times a year and is managed by a highly trusted manager, then I see no benefit. Whereas the benefit to privacy of not having one is significant.