I don't work on Android, but I suspect it's a whole lot less work for both confidentiality and maintenance to not have to worry about daily/weekly OSS releases. That's probably worth more to the decisionmakers than the value of random contributions from people who aren't already inside the partner tent.

[edit] based on the other comments, I surmise that public pushes were already infrequent.

> the result is still open, but the development process is not.

Is the source code available at all times? This is a genuine question, I don't know right now.