Because, see, there's no studio system anymore. Every project gets made on its own, and the budget goes where it goes. In theory, with all the money floating within the current studio system, there shouldn't be a movie that is flat-out terrible. Face it, gentle readers. Even Mr. Roarke couldn't pull off that fantasy.
Bad movies are bad, plain and simple.
Unless they're so bad, they become laughable. Then you can at least rationalize sitting through it, if only for the giggles. But, wait, you say. That it is, folks. Look it up.