You can create closed-source software using open-source software. That’s how Google made so many billions and that’s probably why the AGPL exists.
GCC was so revolutionary because it brought a pro-level (although not at the start) compiler toolchain for free and allowed developers who were so inclined to improve and modify it.
And lots of Python code is for things like machine learning, Go runs lots of DevOps/neo-infrastructure stuff, and I can’t comment on Twisted.
And even most Go software is proprietary, hidden behind Google's bar.