Nepal's ex-PM Oli arrested over deaths during Gen Z protests

Wild how Gen Z protests are shaking up politics worldwide Nepal’s leadership literally getting arrested feels like history moving in real time.

Oli belonged to the Communist Party of Nepal. They arrested the ex PM of the party which holds the beacon of democracy whenever they are not in power. What happens to them when they get power? Why does communist party become authoritarian as soon as they get power? In USA and Europe the people in forefront for more power and democracy and rights are the people from the left. I can’t understand this dichotomy