I don’t see a lot of movies, so I may be wrong about this — but I feel that the profanity trend may have diminished. Movies like Iron Man or The Dark Knight had virtually no profanity. On the other hand, I recently re-watched some movies from the 1980’s (Ferris Bueller, etc.) and I was really surprised at the gratuitous language. I think the urge back then was to appear “cool” by having a foul mouth. Nowadays that is such old hat, that there is no perceived benefit to swearing, so it gets dropped (somewhat).
Also Ferris was about teens who actively try look cool.