Nobody sets out to make a deliberately bad movie. At least, you would hope so.
Every feature film production always begins with a huge level of optimism as the creative team sets about attempting to make the best possible work of cinema that they are capable of. Unfortunately, it doesn't always turn out that way.
With The Room now back in the zeitgeist thanks to James Franco's The Disaster Artist, more people than ever can appreciate Tommy Wiseau's misguided ambition. Sure, the guy made an unmitigated disaster that turned out to be one of the worst movies ever made, but it's not like he did it on purpose. Wiseau genuinely thought he was making a work of art.
Then you get guys like Uwe Boll and McG. Between them they have never made a good movie, but both directors are confident enough in their abilities that they continue to try, even though many people wish they wouldn't. If you asked them, they would likely defend each and every one of their movies to the hilt.
Sometimes, a bad movie can feature a scene or moment so unique, thrilling or exciting that it becomes a source of the frustration that the rest of the project can't tap into that potential. Offering a glimmer of hope in the midst of mediocrity, mundanity and malaise, these moments are the definition of cinematic turd-polishing.