[jimnotgym]

Because not all spreadsheets are audited? Just because they can doesn't mean they are. Also a financial audit is very different in what it is looking for, compared to a cyber security audit, for instance. They are looking to prove the accounts show a true and fair view of the company, not 'are your formulas perfect'. They are more likely to copy out your raw data and run their own analysis.

Answering your edit, not all spreadsheets are opaque either. We design ours to be audited.