Everyone is acting like this is obviously wrong, and they clearly should have communicated the change and made it visible in the exclusion settings.
However, there is a very good reason for not backing up what is in effect network attached storage. Particularly for OneDrive, as it often adds company SharePoint sites you open files from as mountpoints under your OneDrive folder (business OneDrive is basically a personal Sharepoint site under the hood). Trying to back them up would result in downloading potentially hundreds of gigabytes of files to the desktop only to them reupload them to OneDrive. That would also likely trigger data exfiltration flags at your corporate IT.
A Dropbox/OneDrive/Drive/etc folder is a network mount point by another name. (Many of them are not implemented as FUSE mounts or equivalent OS API, not folders on disk.) It's fundamentally reasonable for software that promises backing up the local disk not to backup whatever network drives you happen to have signed in/mounted.
However, there is a very good reason for not backing up what is in effect network attached storage. Particularly for OneDrive, as it often adds company SharePoint sites you open files from as mountpoints under your OneDrive folder (business OneDrive is basically a personal Sharepoint site under the hood). Trying to back them up would result in downloading potentially hundreds of gigabytes of files to the desktop only to them reupload them to OneDrive. That would also likely trigger data exfiltration flags at your corporate IT.
A Dropbox/OneDrive/Drive/etc folder is a network mount point by another name. (Many of them are not implemented as FUSE mounts or equivalent OS API, not folders on disk.) It's fundamentally reasonable for software that promises backing up the local disk not to backup whatever network drives you happen to have signed in/mounted.