Why is the whole country full of Shandong people who used to travel to Kanto, and now they come back to their hometown and meet four people who speak Northeast dialect, all of whom are Shandong people

Why is the whole country full of Shandong people who used to travel to Kanto, and now they come back to their hometown and meet four people who speak Northeast dialect, all of whom are Shandong people? In the past, Hebei and Shandong were treasures with superior natural environment, so the population developed rapidly, while the northeast was sparsely populated because it was located in the cold virgin forest. Even in this developing society, people don't want to live there, but people are forced to go to the northeast because of war or natural disasters. Therefore, many of the ancestral homes of the Northeast people are from Shandong, Hebei.