A government report in December found that the Seattle region needs 156,000 more affordable housing units, and will need 88,000 more by 2040 if the region’s growth continues. Ruth Fremson/The New York Times

The Seattle area, home to both Microsoft and Amazon, is a potent symbol of the affordable housing crisis that has followed the explosive growth of tech hubs. Now Microsoft, arguing that the industry has an interest and responsibility to help people left behind in communities transformed by the boom, is putting up $500 million to help address the problem...