There are lot of people in low density who would _like_ to be in high density. However, these places are absurdly expensive (despite often being more efficient

There are lot of people in low density who would _like_ to be in high density. However, these places are absurdly expensive (despite often being more efficient and cheaper to provide with services) because they've been illegal to build for 70 years, so the stock has been stagnant or declined while the population has grown.