Music being "good" is subjective. A programming language, however, can objectively be better if it allows a subset of programmers to better solve certain problems.
The reason for why OCaml is not more popular, thus, is that this subset is small. The reason for this may be either (a) habit or (b) it's not that much better than other languages. I'm gravitating to (b). OCaml guys seem to be quite dogmatic for the wrong reasons.