Building only affordable housing is how you get cities into a downward spiral. The people who want luxury housing are the well-to-do. They probably contribute 10x the sales tax per capita than the people who live in affordable housing. And almost by definition luxury housing causes more property tax to be paid to cities than affordable housing. Both sales tax and property tax revenues shrink. And the city gets into a fiscal crisis. The city reduces services. People leave. Housing becomes more affordable but also more undesirable.