Indeed, GitHub URLs contain the name of the organization. No need to visit the organization’s page, the org name is visible on each page of the project.
I’m not just trolling here 
, I’m also serious about this issue: a simple contributor editing source code won’t know which modules come from which vendor. They won’t be able to associate the quality or style of some module with Jane Street. It’s poor branding, and not for Jane Street in particular but for all publishers of OCaml source code.
There are also technical merits to having proper namespaces. Those were already discussed elsewhere.