It's worth reading into the history of OSS. There was a bit of sharing going on in the early 70's, but it was all being locked down before Richard Stallman and his contemporaries created the modern OSS movement via the GNU project.
The term "free software" predates "open source" by many years. Stallman started work on free software (the movement and the code) many, many years before Eric S Raymond coined the term "open source".
The terms "free software" and "open source" were created very deliberately to express different values. The conflict between those values has been the source of a lot of contention in the past. Nowadays there's less of that, probably because as the industry grows, the proportion of developers who are old enough to remember this stuff is going down.
https://en.wikipedia.org/wiki/History_of_free_and_open-sourc...