The fact that the company behind rethinkdb went out of business and the community has been unable to keep it alive?
https://github.com/rethinkdb/rethinkdb-python/commits/master https://github.com/rethinkdb/rethinkdb-rs/commits/next
Sure, that's not a ton of development, but at least it's actually, really, open source.
In addition, the software itself doesn't really need much improvement. It does what it's supposed to do very well and the client libraries are fantastic.