Not necessarily. E.g. SML has had multicore since forever. In OCaml it’s the hot new thing now, which probably needs some time in the wild before everything is ironed out.
Back when I was more into looking at this kind of thing (uh, 20 years ago?) I wrote a few simple programs in SML/NJ and far preferred its syntax to OCaml. But even back then, OCaml had more dev community momentum. (Actually Haskell seemed to have even more momentum but I never ever found it readable or comprehensible as a mere mortal.)
At the time for what I was doing, I really wanted... SML but without a garbage collector, operating for systems level programming. And so I was excited when Graydon Hoare started what became Rust. Which is what I prefer to work in these days.
Still, if I wanted a language for higher level development, I really would prefer to reach for something in the ML family of languages, they are just very expressive. But I wouldn't do this for paid employment work, too esoteric. Maybe that will change a bit now that Rust has brought some concepts and syntax from ML to the mainstream.
Can anyone say which implementation specifically?