Didn't they try to push some rather questionable licensing terms on react or do I confuse it with a different open source library? If it was then its users almost became another victim of facebook trying out where it can get away with abusing its position.
They did have a license with a clause allowing them to sue or restrict access to it legally, but they changed it to a more permissive one. Also, even if they did try to do anything, no one was stopping you from replacing react with inferno or preact, they have compatible APIs.