The porn film industry is known for using the best and newest tech. Hell, If I owned a startup that was launching a new video format or camera, I would immediately send free or cheap equipment to major porn producers. Porn can make or break new tech.
The benefit of use high-end cameras (like those from Arri) is that they usually have a higher range for ISO (light sensitivity) and aperture, which makes it easier to shoot without setting up lighting for every specific shot. Most people know this from smartphone cameras: Cheap ones struggle in low-light settings while better ones will still be able to produce decent pictures.