Actually that hurts a bit 
. Paperpile has been built from ground up to be collaborative. I think it’s the only solution that scales to dozens of authors. However, Paperpile - at least at the moment - is built for Google Docs. That’s also not by chance because Google Docs is famous and popular for its excellent collaborative features.
So if your collaborators open it in Word and find it to be not collaborative that’s not a flaw in Paperpile.
But we are aware of the real-life issues and that we still live in a Word/EndNote world. I’m linking to this thread here were Word support is discussed: Support for Word Online would be a game changer