C, C++, Fortran are still used, most Python users just don't see it because it's hidden away underneath the calling function.

I've been surprised by the rise of Python in some ways although not at all in others. Languages like C, C++, Fortran, and dare I say it Rust are too low-level in their raw state for numerical computing. You had the US federal government funding language competitions because of this (see: Chapel). Languages like Python and R (and before that things like Lisp) came along and gave people a taste of something different, and it's obvious what people migrated to.

Part of it is timing: multivariate computational statistics (ML/data science/DL/whatever you want to call it) just sort of started taking off in computer science communities before LLVM-based languages like Julia or Nim could get a foothold. OCaml might have fit that niche but never got there because of a desire to take a different path, or take the path more slowly.

So people looked for a nice expressive language, found it in Python, and buried all the messy stuff behind wrapper functions and called it a day. It was furthered along by Matlab being another comparison on the other side -- Python looks kludgy compared to modern Fortran or C, but not compared to Matlab.

All that wrapper time in Python has its costs, so I suspect as limits get pushed further we'll eventually see a migration to something else like Julia or Nim, or something else not on anyone's radar.

One moral to this story is that expressiveness matters. People will go out of their way to avoid talking directly to machines at a low level.