As I said, a shift in demand. Yes, if you increase supply and if nothing else changes there is a decrease in price. But if you increase supply and the area therefor e.g. becomes more popular among people who earn more money or there is more investment in that area, then you have a shift in demand which can lead to an area becoming less affordable. [0]

[0] https://opentextbc.ca/principlesofeconomics/chapter/3-2-shif...