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.