A giant like JP Morgan does it either way. JP Morgan originates mortgages (via Chase Home Finance). It likes to do that in places where the price of homes does not go down. Put it differently, it likes to do that in places with strong NIMBYs. I suspect Citi and Bank of America and Wells Fargo have the same preferences. I'm not sure how these preferences manifest themselves, and I'm also sure they are not doing anything illegal. But they create some market pressure to hinder development.