It's extremely careless, tone deaf and arrogant to skip Favorites "because nobody uses IE anymore." Maybe you don't use IE at home, but business still have to. Web browser bookmarks need to be backed up and synced and IE Favorites would be the most simple and easy to add as a OneDrive folder.
If you are trying to push people to Microsoft Edge, then why not make it easier to automatically sync Edge Bookmarks? Microsoft Edge Favorites syncing would work even for IE users since Edge and IE can be configured in group policy to sync between each other. So, if Edge Favorites were synced to OneDrive, IE Favorites would be backed up by proxy and vice versa. So, yes, IE Favorites can connect to "other browsers" (Microsoft Edge). It isn't "useless."
Ideally, all bookmarks including Chrome could be synced, but IE Favorites are so simple to add as a folder, it seems dumb to have it not included as part of this feature.