"Quite well" by what metric? It shipped on one device. That's pretty much the lowest bar you can imagine! Did it provide any tangible benefit to anyone? Let alone a benefit commensurate with the enormous cost of developing it and continuing to maintain it?

I think it was insane to start a new OS effort written in C/C++. We have plenty of OSes written in C/C++! We know how that story ends. If you're going to spend the effort, at least try a new language that could enable a better security model.

While I agree with the sentiment given my bias towards safe systems languages, Genode OS is pretty much mostly C++, although they added some Ada/SPARK as well, which is relatively recent research OS.