The frame size matters for quality. A full frame ... (
Most of the folks still using film are doing it for a range of reasons not the least bit related to resolution. Here are a few:
Process — There is a certain ethos of film production that some directors and producers aspire to maintain. They believe it gives their work a look, and perhaps a credibility, that they might not achieve digitally. This may be more important with investors than with audiences.
Speed of process — Using film requires many hands, a lab, and more time than video. That can be an aid in the creative process, even if it is more expensive.
People — Some cinematographers and directors are more comfortable working with film. They grew up with it, and really don't want to move to digital late in their careers. As they "age out" and retire, fewer films will be made with real film, and film manufacturers will close their coating alleys.
Technical limitations — Film is slow (has low sensitivity). It forces the use of auxiliary lighting in most circumstances, both to raise exposure levels and control dynamic range. This has workflow consequences, which can be very positive.
"Look" — Although very subjective, film has a characteristic look that cannot be duplicated exactly with digital means. There is grain, color crossover, and extended dynamic range beyond the 12-15 stops of digital video cameras. That can be important in some situations.
Resolution? A 12MP digital camera has more image resolution than most full frame 35mm films. Super 35 camera aperture is 24.89 mm × 18.66 mm, compared to the standard Academy 35 mm film size of 21.95 mm × 16.00 mm. Full frame 35mm film and digital are nominally 36mm x 24mm. So the film frame is in about the same size class as APS-C digital. The film scanners used to transfer film to digital have higher resolution than the film itself.
One of the companies I worked for was owned by the same conglomerate that owned Consolidated Film Industries in Hollywood. CFI made some instructional filmstrips for us back in the early '80s, and I toured their facilities then. In addition to motion picture film processing and printing, they did lots of special effects work, and they transferred films to video for the television studios and network syndicators. I remember their VP of engineering telling me that most of the films they were transferring to analog video would have to be transferred again when digital imaging came of age. His hope was that the original film negatives would survive in storage that long.