The power frequency isn't that relevant for film, since it just powers motors on the cameras and projectors (or often just hand cranked). In fact, prior to the introduction of sound in films, the exact playback speed wasn't as important, and cinemas often varied.

Where it becomes relevant is for television, and in both cases the refresh rate matches the mains frequency. PAL is 50Hz interlaced, and NTSC is 60Hz interlaced.