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.
I posit (c) it’s from France and written mostly by French people and American naturally gravitates towards languages which generate hype in English and preferably from the USA.
Also it didn’t employ a marketing team to work on outreached and write fancy comments here and some people who have used it for 10 minutes are apparently offended by the Pascal-like syntax and can’t stop discussing it on every Ocaml discussion making every actual users tired.
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.