By combining DC and AC onto the same pins, it reduces the part count and weight of bus bars / conductors which run from a car's charging socket and the battery.
NACS is a better user experience for people and significantly so for people with mobility issues, disabilities, etc.
The pre-eminent NACS fast charging network is markedly better than the totality of all CCS1 charging networks.
CCS2 (Europe) has few (if any) of the drawbacks of CCS1.
Is that a good reason to adopt a standard that isn't open? Probably not. Does the average customer cares and will it have an impact on their day to day? Probably not.
EDIT: Seems like NACS is open after all so I don't really understand why we would bother with CCS.
Charging infrastructure sees significantly more duty cycles than an individual car so it makes sense to move the wear part to the vehicle.
It’s annoying that the US will once again be out of sync with the rest of the world, that’s the main drawback.
And in the end it doesn't really matter. I'm not driving my car across the ocean very often. Import processes already tend to make taking a car from one continent to the other a huge hassle, so to the vast majority of people its probably easier to just sell the car in one place and buy another on the other shore.