First of all, Beijing is located in the north of our country, and Liu Zicheng attacks all the way from south to north. However, we can find that in the history of our country for thousands of years, it is difficult to win any uprising that attacks from south to north. Only two uprisings won and seized the imperial power. So this laid the groundwork for Liu Zicheng's failure to enter Beijing.
Second, although Emperor Chongzhen was indifferent and incompetent, the people's lives were still relatively good, and there was no exorbitant taxation, so most people still supported the Ming Dynasty. Before Li Zicheng went to Beijing, in order to get the support of the people, he shouted a very nice slogan, which was very powerful to the people, so someone was cheated by him and strongly supported him. However, after he entered Beijing, he did not fulfill his original promise to the people, and even let them live in dire straits, so he gradually lost the hearts of the people.
Finally, the quality of the troops organized by Li Zicheng is actually very poor, and most of them are mountain thieves. They can only suffer, but they can't share happiness. After Li Zicheng entered Beijing, his troops restrained themselves well at first, but within a few days, they showed their true colors and wantonly burned and looted in Beijing. So the people hated Li Zicheng, rose up in succession and drove him out of Beijing.