Comment by AnthonyMouse

Areas where it is profitable to do this are areas where housing demand is increasing. Which means that anybody who owns property in such an area can sell it for more than they paid for it, move somewhere else and have the significant monetary gain to compensate them for their trouble. And the gain wouldn't exist with stricter zoning because it comes from the fact that your property is worth more when somebody can buy it and build twice as much housing on it.