Theory: Ghost Houses are Illusions

Abstract
Many of the generic Ghost Houses found across the Mario series are fake illusions or manifestations, created by boos, with no real history.

Arguments

 * Argument 1: In any given Mario game, all of the typical ghost houses found within look identical to one-another on the exterior.


 * Argument 2: The Mansions can be found anywhere, in any biome. Some boo-inhabited galaxies in Super Mario Galaxy and Super Mario Galaxy 2 even resemble parts of Ghost Houses as seen in other Mario games, despite being in space.


 * Argument 3: The Boos have complete control over the mansions, and we often see parts of the mansions flat-out disappear or turn into boos when touched by Mario & Co.


 * Argument 4: The layouts of the mansions make no sense as actual homes for living beings, being filled with doors & stairs that lead to nowhere, often having little to no furniture and usually bring maze-like in nature, making them hard to escape.


 * Argument 5: King Boo is shown to have the ability to generate mansions, as we see him do in Luigi’s Mansion and during the final boss battle of Luigi’s Mansion: Dark Moon. The mansion in Luigi’s Mansion is stated to be an illusion, despite the fact that it looks real and can be physically interacted with, much like other ghost houses.


 * Argument 6: Boos don’t like the light and want to remain as pale as possible, as apparently being more pale is better for scaring people. Light can even be fatal to Boos if strong enough. Generating dark, gloomy mansions to live in protects the boos from that.