I agree that the training sets for LLMs have much more training data for Python than for Rust. But C++ has existed before Python I believe. So I doubt there is 2 orders of magnitude of Python code more than C++.

You miss how many fewer programmers were there in the early years, how much of that code was ever public, and even if it was, how useful it was, as C++ has changed drastically since, say, what we used to write in 2001.

It's not just a question of whether there is more actual code in a given language, but how much is available in the public and private training data.

I've done work on reviewing and fine-tuning training data with a couple of providers, and the amount of Python code I got to see at least out-distanced C++ code by far more than 2 orders of magnitude. It could be a heavily biased sample, but I have no problems believing it also could be representative.