I think OCaml is doing pretty well for itself. For example see the graph of package-growth at [1] and the recent news from people at Facebook about Hack and Flow (both in OCaml). Not all repos are on GitHub and it's not really fair to expect them to be — especially for the sake of vanity metrics, such as this visualisation.
In addition, some of the repos that have OCaml code may not be recorded as such. Repos where the 'brains' is in an expressive language might be overshadowed by boilerplate from elsewhere.
Thanks, I was starting to get a bit depressing seeing the stats on the website. In fact, I was shocked to find OCaml so far off from Clojure.
I think the adoption problem for OCaml is compounded because it suffers from lack of stackoverflow hits for any given errors that you might encounter or any given queries you might have. Searching for something as mundane as "how to read large files in OCaml" leads to just a single hit (Streams at OCaml.org) [0].
Also, OCaml needs a "recipe/patterns" book-- on how-to get some of the things done the right way in OCaml.
In addition, some of the repos that have OCaml code may not be recorded as such. Repos where the 'brains' is in an expressive language might be overshadowed by boilerplate from elsewhere.
[1] http://amirchaudhry.com/towards-governance-framework-for-oca...