Well, because for the moment the Wolfram Language has such a small fraction of developer mind-share. Which means that open-sourcing our projects during their a

Well, because for the moment the Wolfram Language has such a small fraction of developer mind-share. Which means that open-sourcing our projects during their actual development isn't worth the significant development cost (an entire toolchain would need to be open-sourced, and documented). And it also is somewhat antithetical to our design process, which is kinda centralized around Stephen himself, who for the most part really does have a good sense of design. I think that could change, though, and then I think there is a really good opportunity to open source more of our stuff and start building stuff collaboratively with a wider community. Especially when our Cloud stuff comes online. Also, I regularly bug Wolfram about open-sourcing some core part of the kernel. He's not in principal against it, but points out that it would cost a lot, buy us nothing in the short term, and fork the language. But I think it'll happen eventually, hopefully sooner rather than later.