I've written about movie spoofs several times on this blog. But why spoof movies? Well, its just fun to do. The writer or director that creates a spoof about a science fiction, horror, or western scenario has to like the genre or the making fun of it wouldn't be good natured. That would ruin the comedy.
In turn, the viewer should like the original genre or the comedic nature of the spoof won't be as funny to him. For example, if you are familiar with the 1950's atomic science fiction, then having fun with it will make more sense to you. That's the way I see it. What about you?