A document-sharing notification is supposed to mean somebody wants to work with you.
That expectation is valuable.
It can also be exploited.
A stranger can create a document, put promotional text or a suspicious link inside it, and share it with an address. The recipient may then receive a notification from a familiar cloud service rather than directly from the promoter.
The infrastructure gives the message a borrowed suit and tie.
Google Drive has built dedicated anti-spam controls around exactly this problem. Its current Drive spam documentation says files and folders that are strongly suspected to be unwanted can be moved automatically into a spam folder. Users can also report shared items as spam. Once there, those items stop generating comment notifications and disappear from ordinary Drive search and suggestions.
That is not a feature built for normal collaboration.
It is a defense against collaboration machinery being used as delivery infrastructure.
The notification is part of the payload
The advertiser does not necessarily need the recipient to browse Drive voluntarily.
The useful part is the sharing event itself.
A legitimate sharing notification carries context: a coworker sent a spreadsheet, a client shared a folder, a friend sent photographs, somebody invited you to edit a draft.
An unsolicited advertiser can try to inherit that attention simply by using the same mechanism.
The cloud provider becomes an unwilling courier.
Sharing is not the same as permission
A person having a Google account does not mean they want arbitrary files shared with them.
Likewise, a business publishing an email address does not imply that every stranger has permission to create documents and repeatedly attach that address to them.
The stronger evidence of abuse is the mismatch between the collaboration feature and the sender’s actual relationship with the recipient: no shared project, no prior exchange, unrelated commercial material, repeated shares, or mass distribution.
Google’s spam view exists partly to restore that distinction.
Genuine cloud collaboration is useful because a share means something.
Spam degrades the signal by treating every address as a possible notification target.
The industrial lesson is familiar by now.
When inboxes become harder to penetrate, the message does not always get better.
Sometimes it simply learns to arrive wearing another application’s badge.