I agree from a technical POV, but there is a social reason (network effect): Swift has Apple-backing, OCaml is not currently supported by any of the big, influential software companies. OCaml's main backer now is Jane Street who do a lot, but is too small, and Facebook's support (via ReasonML) is too half-hearted to be compelling. As a former OCaml programmer, I would not currently bank a career or startup on OCaml. Indeed I've been doing OCaml programming over the last few weeks (and seen the shortcomings of OCaml's current library eco-system vis-a-vis more mainstream languages) in order to interface with a big existing OCaml development, and they told me they decided to move to Rust for all future new developments.

I say this with a heavy heart, as somebody who spent his first decade as a programmer with OCaml.

Interestingly, even in Feb 2021, there is no compelling mainstream alternative to OCaml (in the sense that e.g. Jane Street are using OCaml): Haskell's being lazy, Java/Scala etc as well as F#/C# being JIT'ed make performance predictability difficult. Rust does not have this problem, but for many tasks where software engineering agility is a more important consideration that extreme performance (which might be most in-house business software?), a GC'ed language would appear to be more suitable.

(No language war please ...)