There's a difference between adapting for mirrorless versus adapting for cinema. They're not just throwing on an adapter to change the distance to the focal plane, they're actually rehousing the lens. Usually that means adding a de-clicked aperture and reducing focus breathing. These are all primes, but cine lenses are usually parfocal as well.
To your point, none of those things are important if you're just a regular consumer and taking stills, but they're all really nice to have/important if you're working on a film.
To your point, none of those things are important if you're just a regular consumer and taking stills, but they're all really nice to have/important if you're working on a film.