So...yeah. This is awkward... JS Bin is not written using React. Or Angular. Or Ember. I doubt if it ever will be too.
Mostly because I'm not personally interested, and as you said, when JS Bin launched there was no React. That was 8 years ago. I'm not sure that in 8 years that React will still be around (or maintained activity as it is now). Same goes for all the other frameworks.
I don't think Angular or React will win. I think something new will come along and knock them out of the conversation (again, Backbone is still around, but it's no longer top of the crop).
Also, I'm an old dog, it's hard to train us old dogs 😉