Why single vendor is the new proprietary - OpenSource.net:

The second misconception is that single-vendor Open Source is, somehow, the reasonable and business-conscious way to do Open Source. You should be on board if you want Open Source to win against proprietary software. But those companies are still doing what is, essentially, proprietary software: like the proprietary software companies of the 80s, they very much consider the software being produced as their exclusive property. They still intend to capture all the value that derives from it. And thanks to copyright aggregation or permissive licensing, they still can change the license any time they want. So it’s still proprietary: they just choose, for now, to release their software under an Open Source license.

BlueSky and AT Protocol.