Just 'cause it's open-source doesn't mean there aren't any politics involved in what gets merged or not.
An example:
lmctfy support was added by the Google GCE team a long long time ago and I attended a meetup where the GCE team submitted the pull request right there... it was never merged. Languished for months without any public review comments from Docker maintainers.
I'd never seen anything like this before. Here we have Google engineers integrating their work with Docker on their own time and being completely ignored. Embarrassing is a nice way to put it.
There may have been outside discussions and real issues that made merging a bad idea, but as an OSS project I expect those discussions to happen in the pull request, not in some business meeting. I'm sure any technical issues would have been addressed if there had been any. I'm also sure that the GCE team would have been more than happy to maintain their driver. Politics and open-source are a happy mix.
sources:
https://github.com/docker/docker/pull/4891
https://github.com/docker/docker/issues/4874