The Go seems to be developed for their needs (well it's coming from them). It's simple to learn, it's very opinionated, how code is stored, how it is formatted etc. It seems perfect for a company that gets a lot of college graduates.

Now with Python, they still seem to stick to Python 2.7 and don't show any effort to move. TensorFlow was released for Python 2.7 and only later Python 3 support was added. Grumpy is for Python 2.7 and first issue opened asking about Python 3 support was closed with change in documentation that only Python 2.7 is supported.

To me it seems like they wouldn't stick to Python 2.7 if they were planning on continuing using Python. It seems like it coincides with deprecating Python 2 in 2020.