If zoning can reduce the value of property how can lack of zoning produce the same result?

Zoning determines how land can be used. If a land is zoned for a certain type of commercial, it can be used for stores, etc. If the land is only zoned for residential, only homes can be built there. If the land is in a place where there is a high demand for commercial real estate, rezoning the land so that it cannot be used for commercial purposes could reduce the value. (;