Hey, thanks for the reply.
It's mostly to do with UNIX already containing utilities and systems that facilitate collaboration between different local users. For example, the ACL system of the OS allows other people to access files based on groups and the mail(1) and write(1) programs allow for both asynchronous and synchronous communication.
I think Dennis Ritchie also talked about this in a paper ages ago [1]. But the gist of it is that one of the primary motivations for making UNIX the way it is is to also "create a system where a fellowship could form."
Of course, we're talking about old minicomputers here in the 1970s where it's all local.