Tooling mostly. It was needlessly difficult to make a small project and use dune to build and run it.

Contrast this with Elixir and Rust where the beginner howtos are front and center. Both mix and cargo are amazing tools that are also very easy to use. Dune is rather cryptic and non-obvious.

I'd definitely be much more excited about OCaml if dune and opam had good cheatsheets and proper brief manuals that don't assume anything about the proficiency of the reader.

A lot of educational OCaml material is either old or imprecise.

Again, start with dune. I want a brain-dead intro to it but still it should cover everything it can do, and how.