Wage, measured in $/month Housing cost, measured in $/month Housing cost/sqft measured in ($/month)/sqft Wage/(housing cost/sqft) measured in sqft. Why is s

Wage, measured in $/month Housing cost, measured in $/month Housing cost/sqft measured in ($/month)/sqft Wage/(housing cost/sqft) measured in sqft. Why is sqft a measure of earning potential?