Really? Lots of the most famous Python modules are partially implemented in C(++) for performance reasons too, it's not exclusive to Ruby.

For example, Numpy is 56% C. https://github.com/numpy/numpy

From my own experience with Ruby and MRI, there's quite a strong culture of "transparency of code". It's not unusual if you're really down into some "interesting" problem to delve first into your gems/frameworks, and eventually even into MRI itself. Being a PL polyglot pays off in spades in these cases, since you get a solid understanding of the underpinnings of everything.

Note that there's very rarely any need to go there, but the fact that it's both possible and culturally encouraged makes a huge difference for those of us who've needed it.

From the Python docs:

https://docs.python.org/3/

Extending and Embedding tutorial for C/C++ programmers

Python/C API reference for C/C++ programmers

... right between "Distributing Python Modules" and "FAQs"

I have a talk at a Ruby conference last week and even put a small amount of assembly on the screen... While many Rubyists aren't expert C programmers, they know enough to look at Ruby's source every once in a while to figure out what's going on.