I don't get this reaction.
Apple: here, we're open-sourcing this previously closed-source Apple-specific thing that made Swift better on Apple platforms. We're moving the Apple stuff into a plugin so Windows and Linux can be equal peers to Apple in the new system. We've implemented preliminary support for Windows & Linux and plan to continue work to bring them up to parity.
Hacker News: I believe that this long game of Swift being "good for everything" but "better for Apple platforms" will be detrimental to the language. This does not help the language nor seems to bring more people to the ecosystem.
Like, what more do you want from them? For them to only open-source Swift Build once they've fully implemented complete parity for Windows and Linux? In the years you'd be waiting for full parity, we'd still see this same kind of comment on every story about swift, asking when they're going to open source a production-level build system.