They were one of the first who offered these 0-byte placeholders, and they rely on a kernel driver, which is only available on both Windows and macOS (but not Linux).
OneDrive [0] and Box [1] are moving away from their implementations and switching to Apple's File Provider API. Their motive might be less development effort, and the official API might be good enough. Still, I wonder whether the deprecation of 3rd party kernel extensions might also be a reason to switch to such a "thin client".
Interestingly, Apple did something similar on Windows [2]: They are now using Microsoft's OneDrive implementation for their iCloud file sync client.
Now I am wondering what Dropbox will do. Is maintaining their kernel extension still feasible on macOS?
[0] https://techcommunity.microsoft.com/t5/microsoft-onedrive-bl...
[1] https://blog.box.com/get-more-secure-seamless-box-drive-expe...
[2] https://blogs.windows.com/windowsexperience/2019/06/11/apple...