I started using Python because of Google Wave. Initially stayed with it because of Google App Engine. Before that I was only using C++ for over a decade. When I stopped using GAE I stayed with Python because I noticed that it is such a good tool to easily solve problems, be it managing the OS, building servers and clients, collecting and analyzing data.
I've always used Javascript and have been using a bit of Rust lately.
But I guess what made it "win" lately is IPython/Jupyter and Conda, which enables non-programmers to use Python as a language to express and solve their problems, like Mathematica or MATLAB did for mathematicians and engineers.
So I guess that Google added a bit to its popularity.