The U.S. is building more apartments than it has in half a century, but the poorest people still can’t afford them. The amount of units affordable to the lowest income groups has decreased across the country even as apartment construction has reached a 50-year-high and even as overall rent growth is slowing, according to a report from Harvard’s Joint Center for Housing Studies. There are many reasons for this, the report’s authors explain, but the main one is that new units being produced are on the higher end and not affordable to people with the lowest incomes. Coupled with rent increases and deteriorating buildings, it means the benefits of the housing boom have been uneven. According…