People really misconstrue the relationship between Python and C/C++ in these discussions.

Those libraries didn't spring out of thin air, nor were they ever existing.

People wanted to write and interface in python badly, that's why you have all these libraries with substantial code in another language yet research and development didn't just shift to that language.

TensorFlow is a C++ library with a python wrapping. Pytorch has supported C++ interface for some time now, yet virtually nobody actually uses tensorflow or pytorch in C++ for ML R&D.

If python was fast enough, most would be fine, probably even happy to ditch the C++ backends and have everything in python, but the reverse isn't true. The C++ interface exists, and no-one is using it. C++ is the replaceable part of this equation. Nobody would really care if Rust was used instead.