(post author here)
While I agree that commercial incentives are critical to consider, two caveats I'd add:
1) I think the nature and depth of the incentives problem varies a lot by industry. Social media is a really complex case, for example. But I'm most interested in collaborative productivity tools, where I think many companies are okay being incentivized to build the best product rather than build data moats.
2) Cutthroat commercial incentives aren't the only thing that got us here. There are also tech barriers.
If I was starting a Google Docs competitor today, even if I wanted to make it open, I think it would be hard to pull off. What kind of API would I expose to enable realtime editing with good offline mode and conflict resolution? How would I deal with clients that have slightly different rich text representations than my own?
In an alternate universe where we already had a user-owned "web filesystem" with good answers to these questions, I could just hook up my client to that existing system and not even worry about persistence at all. It needs to be _easier_ for devs to build the right thing for users, not harder. And it needs to be a _better_ experience for end users, not a sacrifice. The convenient thing will win.