That's an example of something Facebook has control over. If someone wants to fork it, they could, but it wouldn't affect the code Facebook is running. A blockchain would differ in the sense that the community/hashpower could decide to do things Facebook doesn't want to do at which point they would effectively lose control of the chain.
Open source makes sense for companies because they want to share the collective engineering efforts - because often times the code itself isn't the thing being monetized directly. In the case of Facebook it's not the code that is worth billions it's the data they horde. In the context of a blockchain that would mean sharing that data with everyone instead of hording it and acting as a middle-man for advertising, which is very much against the business interests of Facebook or any company with that model.
If Facebook’s developer teams have faster build times, they can create more horrible, unethical, revenue generating features per hour.
FB could have kept Buck for themselves but chose not to.
Open source makes sense for companies because they want to share the collective engineering efforts - because often times the code itself isn't the thing being monetized directly. In the case of Facebook it's not the code that is worth billions it's the data they horde. In the context of a blockchain that would mean sharing that data with everyone instead of hording it and acting as a middle-man for advertising, which is very much against the business interests of Facebook or any company with that model.