Correctness can be very difficult in Assembler, Fortran, and C; and consider the complexity of the systems they're implementing. Though a lot of it probably has to do with hiring.
They could probably do a lot better with, say, OCaml or Rust. Jane Street uses OCaml for, presumably, this reason.
Jane Street isn't an HFT firm, though I do agree that OCaml would be a much better language than Java (though the lack of manual GC tuning could be a dealbreaker).
They could probably do a lot better with, say, OCaml or Rust. Jane Street uses OCaml for, presumably, this reason.