It a lot of factors but the main drivers are inflation and desirability. In places where the desirability is basically neutral, houses do what you would expect and “used” ones sell at a moderate discount to new construction.
Land itself is cheap as dirt.
Level land in Wyoming for $350/acre (so $70/house at median lot size). [1]
(Does it lack transportation, utilities, stores, schools, and jobs? Yes. Because those make land valuable.)
[1] https://www.land.com/property/80-acres-in-Sweetwater-County-...
They’re making more useable land.
Sprawl in NYC wouldn't create more Times Squares, so in this sense, "they aren't making more land".
There's plenty of land in Siberia. There are very few locations that are in the middle of dense cities.