It's not that I write the whole program in another language, it's that I either write the bottleneck in another language (usually Cython), or it turns out that the Python package I'm calling already has its bottlenecks written in another language, whether I wrote it or not.

Day to day, I'm writing Python code which is actually parallel because a large fraction of the run time is dominated by the by things that aren't pure Python. I suspect this is true even for people who are not going out of their way to make it true. It's simply the case that most RDBM systems, Fourier transforms, etc with Python bindings are not written in Python.

The GIL sounds scary, but I think people overestimate the fraction of time it is actually held in their code.