It is amazing to me that slums can even exist in a high cost of living city, where land is so expensive. You would have thought that given how scarce (expensive) the land is, it would be used most efficiently, with all buildings tending to be in top-notch condition and everywhere being fairly tidy and safe.

Basically, if you are the owner of a slum, it seems like it should make economic sense to sell the land to someone else as the value of the land would be higher than the value of the slum.

Why is the market not resulting in what I described?