F# was never really "OCaml on .NET", though, not really. ML on .NET, sure, but it is (and always has been) missing OCaml's most interesting features, such as functors and OO with inferred row-types.
They have kinda positioned themselves that way and had (have?) syntactic compatibility with a subset of OCaml. And OCaml is probably the least obscure of the ML language family, so it's not exactly surprising.