I researched this out of curiosity. It looks like their original intention was to be "open" in the sense of collaborating with universities and researchers. I'm not sure to what extent that still happens, or ever did. But sounds like their closed nature is likely due to two factors. The first is their transition to a for-profit company and outside investment from large corps like Microsoft. The other is their fear of their tooling being used maliciously - which it certainly would, but I'm not sure how justified that is.