Xi Jinping's message to Hong Kong: You're stuck with Carrie Lam
https://edition-m.cnn.com/2019/11/05/asia/hong-kong-carrie-lam-xi-jinping-intl-hnk/index.html?r=https%3A%2F%2Fedition.cnn.com%2F
Even if Beijing choose the next leader, he/she must be backlashed by democratic protesters. That's because many people think the central government must choose the one that carries out strict crackdown.
So, Xi chose the way that doesn't make the movement worse without compromising.