Modern technology allows permanent structures to be much more space-efficient for housing by building many stories high. However, the use of such technology is often banned and structures are limited to one or two stories. Also, even for one-story structures, rules often require eg. 6000 sqft of land to be used for a 1500 sqft house. These rules all result in significant surplus land wealth being required (or expensively rented) for people to obtain permanent housing.
Is it any wonder that, faced with these constraints, people are choosing to live in one-story homes on free land? Government policy is practically begging for it.