It's pretty obvious actually. They want memory safety and predictable, good performance. Rust is the goto language for that in sysdev today. Go is a much better candidate than the ones you mention, but there are legitimate reasons to want to avoid GC.
Additionally, the intersection of people who are interested in working on low level system daemons and people who prefer Haskell/OCaml must be pretty small compared to Rust.
I didn't downvote your original post, but I just think these "why did they use language X instead of Y?" questions are kinda boring and tiresome, for the most part.
If your goal is memory safety, Rust is a good choice. If you additionally want something mainstream (such that it's unlikely that you'll have trouble finding contributors or future maintainers), Rust is also a good choice, and Haskell and OCaml probably aren't. And who knows, perhaps the people building this were just familiar with Rust, but not Haskell or OCaml.
But really, "It's unclear why X was chosen over Y or Z" is just not interesting. If the article doesn't say why, then we're just speculating. And in this particular case, I think the answer is probably pretty simple, obvious, and boring, anyway; I don't think it's "unclear" at all.
The idea that Rust is more mainstream than Haskell or OCaml sounds pretty crazy. I like the language but it's much younger and you don't see established companies using it the same way.
Apple does use Rust in production. Netflix is the only FAANG I’m unsure of if they use Rust anywhere or not. Three of the five companies are platinum members of the foundation, even.
There are stirrings of Rust module support in the FreeBSD kernel, which is heavily used at Netflix, so it's possible there'll be some Rust over there too, soon.
Performance being important in system development is pretty much a given, and doesn't necessarily even need to be mentioned. You could argue that systems software is well defined as software where security, performance, and stability are more important than all other concerns.
I think the fact that your comment didn't elaborate is why you're being downvoted, not for asking questions. It can be interpreted as a question, but it can also easily be interpreted as a shallow dismissal of their choice of Rust, which is a fairy common thing on HN. If you had laid out some details on why the choice puzzled you, your comment would probably have been interpreted more charitably.
I think consistency is more important than actual execution time. Python will certainly have more latency responding to time queries, but it will be consistent and likely indistinguishable from a faster program.
