Economies of scale and network effects.
Nothing has to be the standard. But if 80% of people are familiar with X, choosing Y incurs friction.
For instance, there is an enormous benefit to the entire world from using a standard IP/TCP stack. Yet, we don't seem to suffer from a centralized authority making controversial or conflict-of-interest decisions regarding that stack.
So what I was suggesting is that document-editing abide by some global protocol/standard, which would include storage, versioning, and permissions. As far as the choice of user-facing interfaces and implementations of logic around those standards, there need not be just one, or even a few. Everyone can bring something cool to the table and anyone can use whichever flavor they wish.
It's a solution that works for anyone with basic IT skills. Offer your extended family access, and use the provided software to control permissions etc