Housing is not zero sum at current US density levels. You can put one house on a half acre or you can put 3-4 10-story apartment buildings on it with 20 3-bedrooms each. We immorally choose to have a housing shortage to keep the poors out.
You can't start a company that says "let's increase the supply of housing because demand is high." You can do that with most other markets.
What I think you're saying is it ought to not be zero-sum because there's enough land - perhaps. I was talking about the ability of market participants to increase supply.