Your thought process is completely fair, but just to clarify: Phabricator was never open-sourced by Facebook. The main engineer behind Phabricator (Evan Priestley) left Facebook to create Phacility and open-source Phabricator; that was never a Facebook product.
If memory serves, Evan open sourced Phabricator at Facebook back in 2010 or 2011, then quit to work on it full time.
Shortly after (months, years?) the internal version of Phabricator diverged from the now not FB managed or stewarded OSS one.
However I think it is fair to say, assuming my memory is correct, that Phabricator was open sourced by Facebook at a very different time, before the company really committed to supporting open source projects. At that time it was more ‘if an individual engineer wanted to then go for it’ rather than there being any formal process or consideration of longer term commitments.
That changed fairly shortly afterwards with the creation of the OSS team.
I remember someone transitioning to the newly formed team and moving from Dublin to London to do so in ~2012, as we became housemates :)
> left Facebook in April [2011], and shortly after, we open sourced Phabricator
Although if Evan had access to the codebase after he was an employee and if it was the Facebook codebase that was open sourced then Facebook were involved. The original post sounded (to me) like the OSS code wasn’t the same as the FB code.
I think that just backs up my point that it was the Wild West back then in terms of individual decision making.