The only way to really open source a hardware project of this magnitude is to set open source as a constraint from the start. If you don’t, you inevitably end up with someone licensing some code somewhere from a vendor that can’t be open sourced. It gets integrated deeply enough that the project can’t exist without that piece and it’s too late to rewrite around it so the open source commitment goes out the window.
If I had to guess, it sounds like Valve tried to work around the situation with the workshop where participants entered into some contract as part of the workshop.
And if I had to guess about the Facebook situation, it was probably decided to open source the project after the fact. I’m guessing they wrote the website copy while someone else went off to try to secure open source permission for all components involved and they never reconciled the two efforts, hence the weird dead eBay links and missing files.
It's the same model as any game-console SDK. If you ask for changes to the SDK, those changes are going into "the SDK", which all customers get access to. Platform providers don't tend to offer work-for-hire for custom forks of their code; instead, what they're offering is to prioritize adding certain features to the shared upstream codebase. In the end, the platform provider wants there to just be one SDK, that solves the superset of all their customers' problems. Anything else is a ridiculously-large maintenance burden.
where if you wanted a tracker that wasn't a full controller you had to build it yourself. This involved a paid workshop in Seattle to get access to the dev kit and learn their tooling. Hardware was open source, but firmware was closed. If you wanted firmware changes you had to pay Synapse consulting fees for them to do it for you, and the updated firmware would then be made available free of charge to anyone else who paid for the workshop.