According to the USD economist quoted in the article:
“The people who are leaving are likely the lower-income to middle-income categories,” said Alan Gin, an economist at the University of San Diego. “They want to leave because they can’t afford housing.”
Since housing price in San Diego has been increasing between 2015 and 2024, while there’s a net out migration between that same period tells me that more people are moving out than moving in, but the people moving in makes more money and can afford buying at the current price.
