Exploitation for the last 3 decades - the "Grindhouse" theatre of today

How do you explain how sub-sub-sub par movies like White Chicks, Epic Movie, Kicking & Screaming and Norbit make money - well, by definition they are exploitation movies :

Here's the definition of "exploitation films" from Ephraim Katz's beyond-first-class Film Encyclopedia :

"Films made with little or no attention to quality or artistic merit but with an eye to a quick profit, usually via high-pressure sales and promotion techniques emphasizing some sensational aspect of the product."

Remember, no one sets out to make a bad movie, but it happens. Being an amateur film-maker I can understand when things don't go as planned. But making over $100 million dollars on movies that would have played to grindhouse theatres in the 70's doesn't make sense to me.