Why are there so many Shanghainese in Chongqing?

There are many middle-aged people from Shanghai in Chongqing (that is, people born between 1930 and 1949). I have a neighbor in Shanghai, surnamed Lin, male, born in 1940. My hometown is in Shanghai, but I have been working in Chongqing. He is a pharmacist. Compared with young people who are twenty years younger than him (that is, people born after 1960), he has no interest in the story of love between men and women. Apart from his close relationship with his wife, he seldom deals with outsiders. His face was never full of emotions, and he always maintained a quiet, thoughtful, serious and solemn expression. I+0988.50086 Miss Lin is not interested in meeting me or other children. He gave me the impression that he was calm, thoughtful, without emotion, desire and pursuit. He never comments on others, and no one has ever commented on him. He has never been influenced by the bad social atmosphere and kept his innocence. I like Mr. Lin, a middle-aged man and a real Shanghainese!