Plus the developers need to be able to make a profit after accounting for operational expenses, closing costs, etc. If there's no financial incentive, nobody is going to build houses.
This myth of zoning being the only factor is maddening. It's almost like the California folks think their housing market is the only one. Plenty of jurisdictions have loose zoning laws and we still see skyrocketing property values. There's interest rates and inflation to consider.
The cold hard truth is: when a bunch of people all want to live in the same areas, housing is going to be expensive. There's no way around it.