Congratulations on recognising that your glib generalization above was wrong! Now see if you can imagine any way in which development of a neighbourhood can ever increase demand. An idea to get you started: there exist people who would like to live in a nice apartment but who would not be interested in an old rooming house. There exist people who only want to live somewhere that already has residents at their (higher) income level. There exist services that are only offered in areas that have people with x disposable income. And there exist people that will only move somewhere that said services exist.