alt Hacker NewsEven if there isn't any 3rd party code, the whole process of going through the codebase to confirm there really isn't any 3rd party code, and generally getting the legal department to sign off on it, is a lot of work in itself. My impression is that this kind of "historic source" release typically only happens if somebody sufficiently senior in the company cares enough to actively push it through. The default is that nobody does care that much, and it doesn't happen.
"Do nothing" has essentially zero downside for a big company that happens to have something of niche interest like this in its vaults.
third-party code is one thing, political correctness is another. What was acceptable in 90s brogrammer culture may not be considered acceptable by PR obsessed corporate types now.
To put this more charitably, the only reason to release something like this is to get some good PR, but if not carefully controlled, such a release could create more bad PR than good PR.