I just use the OCaml Platform VSCode extension: (https://marketplace.visualstudio.com/items?itemName=ocamllab...) or the OCaml LSP server: https://github.com/ocaml/ocaml-lsp in other editors and don't really need anything domain specific.

Vim/Emacs/Sublime (And now things like VSC/Helix) are more than sufficient for coding without an IDE. Autocomplete scripts, the terminal, build scripts, etc work great. Now with LSP you can turn any editor into an IDE pretty trivially.

You answered it yourself. More mainstream languages have specific IDEs and OCaml is not more mainstream.