Wiring may exist but wouldn't it require significant mods to install multiple cameras? Is something like that really worth it?
installing after the car's been shipped would be quite an effort, sure. But KIA specializes in minimizing production costs by having as few variations/production lines as possible, and sharing as many components as possible. That's why you don't tick individual packages and options with Kia, you just select the trim, the colour, and that's basically it.
They aren't producing 2 different bumpers just for the 360 camera or not, they have one bumper, and the ones without the 360 camera just have a blank insert. the extra cost is now you have to take apart a fully assembled car to add it on, instead of simply having it installed during production.