I come from Chengde, Hebei. Why do we only speak Mandarin?

Chengde dialect is based on Beijing dialect, which is influenced by Huang Zhuang, the Ministry of Internal Affairs and the Manchu garrison during the development of Chengde. Different from Beijing dialect, Chengde was later influenced by a large number of immigrants from northeast Shandong and Shanxi, which made the Beijing flavor in Chengde dialect fade, only retaining the pronunciation standard of Beijing Mandarin, but at the same time it became lost. Chengde dialect also has many elements that Beijing dialect does not have: for example, making trouble and slapping in the face is called fighting, which is Shanxi dialect. The forehead is called Yuegai, and the doctor is called Zhagu, which is a Shandong dialect. Gaha, shaking his nose, kicking and screaming, this is Northeast dialect. When collecting standard sounds, dialects are not reflected, so the impression is Mandarin. In fact, there is a difference between the elderly in Chengde and Mandarin. Chengde dialect is a variant of Beijing dialect. The taste of Beijing has faded, but it has changed. We didn't collect these dialects when we collected them. Of course, only standard Mandarin is left. Chifeng, a neighbor of Chengde, with a large number of Shandong immigrants, sounds worse than Chengde dialect (Fan Wei dialect). Old Beijingers look down on Chengde people. There used to be a saying in Beijing that "it is better to quarrel with Beijingers than with foreigners". But I love listening to Chengde dialect! It's rare for children to smell this!