Its mostly about practicality. Haskell is kind of pain when you need IO, as in when you go there there is no way out.
Ocaml is more practical, and less punishing (you can do IO without monads), but the most important diffrence is performance. Haskell is VERY hard to make predictable because its lazy. Ocaml is strict so general system performance is much easier to predict.
But they are sibling languages in my book, while i still prefer ocaml over haskell.
Also IMO the dev tooling is better for OCaml. Far better compile times.
A big part of interacting with APIs (which I imagine Stategraph does) is just dealing with records, and working with records in Haskell is really annoying unless you bring in lenses which bring a lot of complexity.
Ocaml is more practical, and less punishing (you can do IO without monads), but the most important diffrence is performance. Haskell is VERY hard to make predictable because its lazy. Ocaml is strict so general system performance is much easier to predict.
But they are sibling languages in my book, while i still prefer ocaml over haskell.