They do not have to use those reflex cameras they never get printed at max resolution anyway. Those silly little computers can take hundreds of pictures in the time it takes that reflex lens camera to shoot one.
They used to use pencil and paper.
They’re not shooting for max resolution , you’re right. But they are shooting for just the right moment in time, hence, those cameras that can shoot 12-14 fps, sustained over a large number of exposures. Phones and mirrorless can’t do that, at that level. Shoot an Alexa, Red, etc and just pull frames from the video, as long as you don’t need quick focusing. They’re using the best tools for their jobs, so, clakity-clack.