Why does everyone say that Shanghainese are the smartest people in China? Please explain.

There are few locals in Shanghai, and Shanghai is basically an immigrant city. It happens that smart people gather here, because it has a good geographical location and is also the mouth of the Yangtze River. However, Jiangsu, Zhejiang and Shanghai have been the places with the most literati since ancient times, and the brain capacity here is very large (look carefully, there are many big heads). However, people nurtured in the Shanghai environment are really "civilized". At least we can see that they are different from other places in dressing and manners.