Probably true, but that is probably also against the license agreement (even if unenforcable). Most companies don't want to take this risk (and potential legal costs) just to release code that won't bring them any (direct) revenue.

That's not the same thing - one is redistributing the API (which is what we're talking about here) and the other is implementing an API.

To be clear we are talking about releasing code which calls into an API. Agreed you can't redistribute somebody else's SDK without permission.

To use bullet physics as a hypothetical example, if my game was the hello world example [0], I would expect that practically that entire file would be un-distributable.

[0] https://github.com/bulletphysics/bullet3/blob/master/example...