I think that the nature of a wiki is inherently centralised. You want a central, curated wiki, not one that has a thousand different versions, each of which needs to be mixed together, and checked. Otherwise, you'll have quite the time dealing with conflicts and things.
But the upside of a wiki is that it can be self-hosted. If a current wiki isn't good enough, you are able to host your own, and work from that instead. Issue is that it's not great if you're technically inclined, and it's a lot easier to host/manage a wiki that someone else hosts, tying it all the way back to a single central service.