depends on what you mean by falling off
wachowski trannie brothers aren't bad directors, they just make bad movies
cloud atlas didn't look bad, it was just a shytty movie, the story wasn't interesting or told in an interesting way
they are the reverse George lucas, where they need to stick to directing and have someone else write/ come up with the ideas
spike lee to me is still a good director, he's just made some bad choices into what films to make, sometimes you need to know how to fall back, and not try to do everything yourself
james Cameron ain't fall off, I couldn't even finish avatar, shyt looked like a videogame cutscene, but I think he had developed brand new film technology just for the film, so you can't say he fell off as a director
so it's all relative
When a film is bad, I blame the producers first, if pacing is off and the overall look of film is trash I blame the director, if the characters interactions are lifeless and unbelievable I blame the actors