The counter to that is that TypeScript is Apache-licensed. However, you can't erase history by throwing up a Github repo.
Moreover, I'm hearing more people say they don't trust relying on a big corp for their client-framework. I think many don't disagree with that idea, but more or less trust Google, so they embrace Angular with prejudice. Anything with Microsoft's signature feels less open, and may push some past that tipping point.