1. To have only his subject in focus.
2. The leftist editors are always looking for the worst possible pictures to use of repubs, the best of dems, so you want to have as many as possible for them to select from.
A difference of a part of a second can make a big difference in facial expression.
Yes, that's his claim - low depth of field. But his other settings were 3 stops beyond the large aperture f-stop/low depth of field setting that he used (maybe the cameras limit), and that gave him either a dark exposure or a grainy exposure if his ISO setting compensated for the darkness. He'd have had the same depth of field at 1/1000th of a second, and that would have been the proper lighting; not too dark. As it was he fixed his otherwise low light (high shutter speed) exposure with a grainy ISO setting, or fixed the end product with photoshop. I would think using a high ISO setting would be embarrassing for a professional if he didn't have a good reason to use it.
2. The leftist editors are always looking for the worst possible pictures to use of repubs, the best of dems, so you want to have as many as possible for them to select from.
Yes, that's for sure. He was shooting at 30 frames per second (or 20 fps according to other accounts). That gives him lots of images in a short period of time, and gives him a good selection of best & worst facial expressions if that's the goal, but with the Pro camera the fps rate has no bearing on his aperture and shutter speed settings.
Bottom line, the photographer chose either a dark exposure or an image on the grainy side, sacrificing quality, to get a stop-action shot.