Pooge parent
A spreadsheet doesn't scale, is easily lost or corrupted or stolen, doesn't have security and people that tend to use it don't add data validation and don't care about atomic properties or data consistency.
These are different reasons than given previously. Regardless, Google Sheets are automatically versioned and have extensive access controls, both at the document level, and cell level. Further still, these types of documents are not black boxes, since anyone with access can inspect the data themselves. Arguments regarding scale and atomic operations/properties/consistency are fine, though I do not believe all business logic is necessarily beholden to these qualities.
Let's qualify spreadsheets as software: critical software should not be made by a non-technical person that doesn't know software engineering principles.
I guess Google Sheets invalidates some of my arguments, but Excel certainly does not. And, even if the feature is there, I've never seen them applied.