(quoting the manual: « When pinning a package, the source is searched for metadata in an opam or <pkgname>.opam file, either at the root of the source tree or in an opam directory. »)
I don’t know what the maintainer’s opinions is, I still have to ask, but on subjective aesthetic grounds, I wouldn’t want an opam file in the root directory of a project whose main focus is really C, C++, and maybe python. It’s kind of messy from that perspective. Maybe I’m totally off base.