IMHO, Google released Tensorflow because AI is currently being driven by research, and researchers were mostly writing code for Torch that is used at Facebook. So FB folks were enjoying lots of new algorithms, benchmarked against their systems. Google open-sourcing TF shows that benefits of open-source outweigh the disadvantages of being closed source. Even if the future is data and not code, companies will not open-source their code if they have nothing to benefit.