> It just shows the mindset of its devs was a little behind the realities of the industry, or they simply didn't care about concurrency.

OCaml cared about concurrency (e.g. Lwt, Async are old libraries that provide concurrency -- they didn't need multicore Ocaml). OCaml didn't care so much about true _parallelism_ in threads until recently. Parallelism was to be obtained via processes and not threads in pre OCaml 5.0. True parallelism in threads is available in OCaml >= 5.0

Python is actually trying to go multicore too ! OCaml however beat it to the punch. The strengths of Python are elsewhere though, a topic for another day.