One hypothesis I considered is that some contributions have moved away from the opam-repository and are happening directly in npm, thanks to esy. I ran a similar analysis (logs) on all npm packages tagged ocaml, but the results are unconclusive (I may be missing more OCaml package on npm that is not tagged).
npm “ocaml” contributors
npm “ocaml” commits
(If you wonder what’s the long trail between 2003 and 2009: this is the development of bs-sedlex, which goes back to an old OCaml-only prototype by Alain Frisch in 2003. There is also a version of OCaml packaged on npm, but I removed it from the analysis as it was adding noise and was mostly not-esy-specific contributions.)
Note that we are talking about ~4K commits here, which remains fairly small compared to the ~120K commits for opam-repository packages on the last year. When I tried to merge both sets together this didn’t make much of a difference compared to just-opam numbers.
Maybe someone should redo the analysis with “reason/rescript” tags in addition, to measure the contribution volume there. I sticked with packages that self-identify as “ocaml” for now.