No users, no walled garden. More users, more walled garden. Is this just the natural state of systems that require/acquire network effects?
This is why we can't have an open libertarian Internet, and instead have walled gardens and moderated forums - ordinary users don't want to deal with the crap.
It's also why we don't have open API's, and why the API's that the big providers do give us tend to be nerfed and then discontinued - they're constantly abused, which imposes a maintenance cost that businesses have to justify.
It's why an email server is so difficult to run and email delivery is so unreliable. It's why you can't (or shouldn't) rely too much on Paypal. It's why governments effectively outsource Internet policing to big providers.
And so on.
I hated the days when you constantly had to switch web browsers to get pages to render. I'm glad it's rare now, because we didn't give up on the hope of open systems.
Mark might have lost the battle to have HTTP/2 encrypted by default, but at least when Let's Encrypt came out, it still worked in all browsers.
Would we have been better to just give up and have lots of walled gardens instead? I don't think so. I'm glad we have WWW.
Personally I don't think XMPP failed because being open made it slow to adapt. I think we're mostly stuck because ICQ, AOL & MSN just got there first.
I don't envy being in Moxie & OWS's position of figuring out how to make this work. I'll add opinion and some of it harsh, though I'll reserve criticism until I've built something as awesomely globally deployed as Signal.