> I found the model especially strange because of the requirement that any custom changes you asked for would be available to everyone else (your competitors).
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.
